Palmaris Longus and Plantaris

Wiedersheim, Robert.  The Structure of Man: An Index to His Past History.  Macmillan, London.  Translated by H. and M. Bernard.  Edited by G. B. Howes.  1895.  A textbook of comparative anatomy from 1895, written in German by the Freiburg professor Robert Wiedersheim and translated into English for medical students.  It sets human anatomy beside that of the apes and lower animals to show the parts that link humans with them, and its editor warns that similar structures can arise independently.  The article quotes it for the claim that the palmaris and plantaris are time honoured examples of gradual degeneration.

1. 1a.

   Page 109:  “The palmaris (= p. longus) and its homologue in the hind-limb, the plantaris, are time honoured (and certainly among the best) examples of the gradual degeneration of a muscle.  The degeneration of the former has not yet proceeded as far as that of the latter, as is most evident in the fact that while the palmaris still reaches the palmar fascia of the hand, the plantaris only in exceptional cases becomes connected with the homologous plantar fascia of the foot, and in doing so regains its former significance as a flexor of that organ.” ↩ ↩

2. 1b.

   Pages 109–110:  “The plantaris must therefore, as an original flexor, have begun to degenerate from the time that the plantar fascia became secondarily attached to the calcaneum, and helped in the formation of the arch of the foot, as the latter became transformed into a supporting organ.”  The page break falls after "have". ↩

3. 1c.

   Page 110:  “But why are the palmaris and plantaris of Anthropoids, in which such transformations do not take place, also in a degenerate condition?  It does not appear difficult to answer this question if we consider that these muscles originally extended, as do their homologues in the lower Mammals, through the mediation of the palmar or plantar fascia to the phalanges, and acted as common flexors of the fingers and toes.”  “the fibrous terminal expansions of the palmaris withdrew more and more from the fingers, and found points of attachment in the palm of the hand and in the ligamentum carpi transversum.”  “The palmaris becoming thus superfluous, is variable and occasionally absent.” ↩ ↩

4. 1d.

   Page 110:  Printed as footnote 2 on that page.  “That it is still functional in the hand is shown by its occurrence, which must still be considered normal.  It is absent on one or both sides in about one in every ten bodies.” ↩

5. 1e.

   Page 201, section B of the Conspectus of the Organs Mentioned in the Text:  “Mm. plantaris and palmaris longus, when completely tendinous.” ↩

6. 1f.

   Page 205:  “The palmaris longus and plantaris muscles furnish a case in point; for while these, and especially the former, are not infrequently so well developed that there can be no doubt of their being functional, cases occur in which one or the other of them has become quite transformed into tendinous tissue and really vestigial.”  Wiedersheim is quoting Osborn here.  “Both in the muscular and skeletal systems we find organs so far on the down grade that they are mere pensioners of the body, drawing pay (i.e. nutrition) for past honourable services without performing any corresponding work — the plantaris and palmaris muscles for example.” ↩ ↩

Coyne, Jerry A.  “Darwin right again: the inner ears of sloths are highly variable.”  Why Evolution Is True (blog).  Aug 5, 2012.  A blog post from 2012 about a study that found more variation in the inner ears of three-toed sloths than in four other mammals, including a squirrel and a mole.  Coyne reads it as support for Darwin's claim that organs no longer needed vary more, and he cites the palmaris as an example.  The article quotes the post for two claims about the palmaris: that it has been reduced, and that it is pretty useless.

1. 2a.

   Paragraph 7:  “The variability of vestigial organs is well known.”  “The palmaris longus muscle has been reduced to a small tendon in our forearm; it's absent in 14% of people and, being pretty useless, is often used for tendon grafts in the wrist.” ↩ ↩ ↩

2. 2b.

   Paragraph 6:  “In the technical jargon of evolutionists, those features are no longer under "stabilizing selection", the kind of natural selection that eliminates deviations from features that are at a local optimum for being fit.” ↩

Gray, Henry.  Anatomy of the Human Body.  Lea & Febiger, Philadelphia.  20th American edition.  Edited by Warren H. Lewis.  1918.  An anatomy book from 1918, first written by Henry Gray and here in its 20th American edition, edited by Warren H. Lewis.  The article quotes its descriptions of the palmaris and the plantaris, and its wording that the plantaris is a rudiment.

1. 3a.

   Page 446:  “The Palmaris longus is a slender, fusiform muscle”.  “It ends in a slender, flattened tendon, which passes over the upper part of the transverse carpal ligament, and is inserted into the central part of the transverse carpal ligament and lower part of the palmar aponeurosis, frequently sending a tendinous slip to the short muscles of the thumb.”  “Variations.—One of the most variable muscles in the body.” ↩ ↩

2. 3b.

   Page 450:  “The Palmaris longus is a flexor of the wrist-joint; it also assists in flexing the elbow.” ↩

3. 3c.

   Page 483:  “It forms a small fusiform belly, from 7 to 10 cm. long, ending in a long slender tendon which crosses obliquely between the two muscles of the calf, and runs along the medial border of the tendo calcaneus, to be inserted with it into the posterior part of the calcaneus.  This muscle is sometimes double, and at other times wanting.” ↩ ↩

4. 3d.

   Page 483:  “The Plantaris is the rudiment of a large muscle which in some of the lower animals is continued over the calcaneus to be inserted into the plantar aponeurosis.  In man it is an accessory to the Gastrocnemius, extending the ankle if the foot be free, or bending the knee if the foot be fixed.” ↩

Coyne, Jerry A.  Why Evolution Is True.  Viking, New York.  2009.  A 2009 book by Jerry Coyne.  The article uses it for Coyne's own definition of a vestige: a trait can be vestigial and functional at the same time.  The book does not discuss either muscle.

1. 4a.

   Page 58:  “But this rejoinder misses the point.  Evolutionary theory doesn't say that vestigial characteristics have no function.  A trait can be vestigial and functional at the same time.  It is vestigial not because it's functionless, but because it no longer performs the function for which it evolved.” ↩ ↩

Gray's Anatomy: The Anatomical Basis of Clinical Practice.  Elsevier.  41st edition.  Edited by Susan Standring.  2016.  The 41st edition of Gray's Anatomy, a clinical anatomy text edited by Susan Standring.  The article uses its modern description of the palmaris longus as a weak wrist flexor that also anchors the skin of the hand.

1. 5a.

   Page 850:  Under the Actions heading of the entry for palmaris longus.  “Palmaris longus is a weak wrist flexor.  Through its insertion in the palmar aponeurosis, it also acts as an anchor for the skin and fascia of the hand against horizontal shearing forces.”  Under the Attachments heading of the same entry.  “Palmaris longus is occasionally absent on one or both sides.” ↩ ↩

Gangata, Hope et al.  “The contribution of the palmaris longus muscle to the strength of thumb abduction.”  Clinical Anatomy 23(4):431–436.  2010.  A 2010 study that measured thumb strength with a dynamometer in 38 people who had the palmaris on one side only, and in 30 others who had it on both sides.  The authors conclude that the muscle helps thumb abduction and urge anatomists and hand surgeons to accept that action.  The article uses it as the measured evidence that the palmaris helps the thumb.

1. 6a.

   Section Abstract:  “Two groups, both right hand dominant, were selected from 1,200 sampled participants.  The first group comprised of 38 subjects with unilateral presence of the PLM and was used to determine the strength of thumb abduction.”  “the force of thumb abduction was significantly greater on the hand with a PLM than the one without it (P = 0.014), irrespective of hand dominance.”  “Thus, 10% was deducted from all the dominant hands, and the force of thumb abduction remained greater on the hand with PLM than the hand without it (P = 0.049).” ↩ ↩ ↩

Sebastin, S. J. et al.  “Does the absence of the palmaris longus affect grip and pinch strength?”  Journal of Hand Surgery (British and European Volume) 30(4):406–408.  2005.  A 2005 study of 418 normal Asian subjects, whose palmaris was checked clinically and whose grip and pinch strength was measured.  It found no difference in strength between people with and without the muscle.  The article uses it for that finding, and for the point that the palmaris tendon is the most frequently harvested tendon in reconstructive surgery.

1. 7a.

   Section Abstract:  “The palmaris longus tendon is the most frequently harvested tendon for reconstructive plastic and hand surgical procedures.”  “the presence or absence of the palmaris longus muscle was clinically determined in 418 normal Asian subjects.  All subjects also had their grip and pinch strengths measured.  No statistically significant difference was seen in the grip or pinch strength measurements between subjects who had a palmaris longus tendon and those who did not.” ↩ ↩ ↩

Cetin, A. et al.  “Prevalence of the palmaris longus muscle and its relationship with grip and pinch strength: a study in a Turkish pediatric population.”  Hand 8(2):215–220.  2013.  A 2013 study of 585 Turkish schoolchildren aged 6 to 11.  Each child was asked to oppose the thumb to the little finger while flexing the wrist, and grip and pinch strength were measured with a dynamometer and a pinch meter.  The muscle was missing from 30.4% of right hands, and its absence did not affect grip.  The article uses it for the grip finding and for the authors' remark that the absence seems to be inherited, though the genetic pattern is unclear.

1. 8a.

   Section Abstract:  “A total of 585 subjects, comprised of 305 males and 280 females, were included in our study.”  “While grip strength of the hand was not affected in the case of absence of the palmaris longus, in both sexes, pinch strength of the fourth and fifth fingers of both hands decreased.” ↩ ↩

2. 8b.

   Section Results:  “No subject with PL absence complained of difficulty performing any task in the study group.” ↩

3. 8c.

   Section Introduction:  “Its absence appears to be hereditary but the genetic transmission is not clear.” ↩

Yammine, Kaissar.  “Clinical prevalence of palmaris longus agenesis: a systematic review and meta-analysis.”  Clinical Anatomy 26(6):709–718.  2013.  A systematic review and pooled meta-analysis of 26 published studies of how often the palmaris longus is absent, grouped by ethnicity.  It found an overall pooled absence of 20.25%, with 2.71% in East and South-East Africans and 41.7% in Arab Middle Eastern samples.  The article uses its pooled rates to support the claim that absence depends on ancestry.

1. 9a.

   Section Abstract:  “We identified 26 articles which met the inclusion criteria.  Meta-analyses showed an overall PLA pooled rate of 20.25%, higher than the commonly reported overall rate of 15%.  Our results also showed significantly lower pooled rates in Africans (11.3%) and East Asians (4.5%) when compared to Arab Middle Eastern population (41.7%).  A subgroup analysis of the African group showed a pooled rate of 2.71%, the lowest, in the East and South East African population.  The pooled rate was 26.3% among Caucasians, 26.16% among South and Southeast Asians and 34.13% among Turkish.” ↩ ↩ ↩

2. 9b.

   Section Abstract:  “No significant differences in PLA rates were found for laterality, gender, the combination of gender and side or the combination of gender and laterality.” ↩

3. 9c.

   Section Abstract:  “The lowest rate of PLA found in East and South East African populations might be indicative of the subsequent phylogenetic degeneration of the palmaris longus muscle in modern humans after the "Out of Africa" migration.” ↩

Vučinić, N. et al.  “Testing the inheritance pattern of palmaris longus muscle absence.”  Surgical and Radiologic Anatomy 47(1):131.  2025.  A family study of 82 people from 20 families, tested with Schaeffer's test, in which the muscle was absent in 59.75% of them.  That rate is far above the 37.5% reported for 800 people in Serbia by Erić and colleagues in 2010, which suggests that families with the trait were over-sampled.  The article uses it for the claim that absence runs in families.

1. 10a.

   Section Abstract:  “A total of 82 individuals (39 males and 43 females) from 20 families, consisting of fathers, mothers, and all their joint offspring, were examined.”  “In 80% of the families (16 out of 20), at least one child exhibited the same trait as a parent, indicating a consistent transmission pattern across generations.  However, in 20% of families (4 out of 20), the trait skipped a generation.” ↩

2. 10b.

   Section Abstract:  “Its absence is known to be inherited, yet the precise mode of genetic transmission remains uncertain.”  “The inheritance pattern aligns with an autosomal dominant transmission model.  The absence of the palmaris longus muscle is likely influenced by a dominant gene exhibiting incomplete penetrance and variable expressivity, or potentially by mutational effects.” ↩ ↩

Yammine, Kaissar et al.  “A Meta-Analysis of the Surgical Availability and Morphology of the Plantaris Tendon.”  Journal of Hand Surgery (Asian-Pacific Volume) 24(2):208–218.  2019.  A meta-analysis that pooled 41 cadaver studies with 10,062 legs to estimate how often the plantaris is present and how long its tendon is.  It found the muscle in about 93% of legs.  The article uses these figures for how common the plantaris is and for its tendon as a surgical graft.

1. 11a.

   Section Abstract:  “It is used as a graft for tendon/ligament repair or reconstruction in hand surgery whenever palmaris longus (PL) is lacking.”  “Data from 41 studies including 10062 leg specimens yielded the following: overall true prevalence ≈ 93%, overall crude prevalence = 90.6%, bilateral prevalence ≈ 92%, significantly more frequent on the right side, no gender significance, and no significant differences between ethnicities except that of Brazilian populations.  The pooled mean length (± SD) of the PM tendon (PT) was 30.63 ± 5.87 cm”.  “with a tendon length double than that of PL along with an acceptable width.”  “The surgical availability of the PM tendon was found stable across human populations; a clinical advantage when compared to the high variability of PL ethnicity-based frequency.” ↩ ↩ ↩

Menton, David N.  “The plantaris and the question of vestigial muscles in man.”  CEN Technical Journal 14(2):50–53.  2000.  A 2000 article in a creationist journal, arguing that the plantaris is a sensory organ and not a useless vestige.  It cites Voss's weights and spindle counts for the muscle, and its reference to Daseler and Anson gives "75 specimens"; the study's title has 750.  The article uses it as the fullest creationist case on the muscle.

1. 12a.

   Page 50:  “If the human body can be shown to have truly useless organs that are a known vestige of once useful organs in a non-human ancestor, this would be evidence for non-human ancestry.” ↩

2. 12b.

   Page 51:  “It seems overwhelmingly likely that any muscle in the body that actually exists in the present, serves some function.” ↩

3. 12c.

   Page 51:  “The tiny muscular belly of the plantaris is only about one-third the length of the belly of the gastrocnemius and is so slender that it has less than 3 percent of the mass of that of the gastrocnemius”. ↩

4. 12d.

   Page 52:  “Cruveilhier first proposed the muscle to be a vestige in man, believing that as our evolutionary ancestors assumed an erect posture, the plantaris lost its original attachment to the bottom of the foot (plantar aponeurosis) and gained a secondary attachment to the calcaneus bone of the heel.”  The comparative sentences carry no reference.  “In many mammals, including apes and many prosimians, the plantaris is indeed attached to the plantar aponeurosis.  In most ruminants and horses, however, the plantaris attaches to the Achilles tendon similar to man.  In some animals, such as the American brown bear, the plantaris is as large as the gastrocnemius.  The simple fact is that a study of the comparative anatomy of mammals reveals no phylogenetically coherent story based on either the size or the location of the attachments of the plantaris.” ↩ ↩ ↩

5. 12e.

   Page 52:  “While the human plantaris muscle is clearly in a position to flex the knee and to plantarflex the foot at the ankle, its motor functions are obviously trivial.” ↩

6. 12f.

   Page 53:  “Voss, for example, measured the combined weight of a human triceps surae to be 824 grams, while that of the plantaris alone measured only 10.5 grams, a ratio of over 78 to 1!”  “The smaller plantaris, however, was found to have 3.7 muscle spindles per gram compared to only 0.67 spindles per gram for the triceps surae, a ratio of over 5.5 to 1 in favour of the plantaris.” ↩ ↩

7. 12g.

   Page 53:  “Since the plantaris may be surgically excised or even missing in an individual without known loss of function, we may conclude that it is not essential to the triceps surae.” ↩

8. 12h.

   Page 53:  “Even now, the proprioceptive function of the plantaris in a parallel muscle combination is not fully understood, nor perhaps even correctly understood.” ↩

Olewnik, Łukasz et al.  “The Plantaris Muscle Is Not Vestigial: Developmental, Comparative, and Functional Evidence for Its Sensorimotor Role.”  Biology 14(6):696.  2025.  A narrative review that gathers developmental, adult, comparative and clinical evidence and argues that the plantaris is not a regressing remnant.  It contains no new data, and its authors admit that functional studies, such as electromyography, are lacking.  The article uses it as the recent case that the muscle is not vestigial, and as the source of its admission that the sensory role is untested.

1. 13a.

   Section Abstract:  “Developmental data reveal that the PM is consistently present during fetal life, with tendon morphology and insertion patterns emerging early and resembling adult anatomical variants.”  “We conclude that the PM should not be regarded as a regressing remnant but as a dynamically adapting structure with potential neuromechanical function.” ↩ ↩

2. 13b.

   Section 3.1:  “One of the earliest large-scale anatomical studies, conducted by Daseler and Anson [1], reported the absence of the PM in 7% of 750 lower limbs.  Harvey et al. [2] similarly noted its absence in 9% of their dissections.  More recent data by Prakash et al. [13] indicated a higher absence rate of 26%”. ↩

3. 13c.

   Section 4.2.4:  “These features, coupled with high rates of anatomical variability, support the theory that the PM is in evolutionary decline, especially when compared to its more robust form in arboreal or cursorial mammals”. ↩

4. 13d.

   Section Limitations:  “First, the lack of functional studies, particularly electromyography (EMG) and in vivo biomechanical analysis, limits the ability to definitively assess the PM's role in movement and proprioception.  Second, comparative anatomical data among mammals often stem from small sample sizes or isolated case studies, reducing generalizability.” ↩ ↩ ↩

Diogo, Rui, and Bernard Wood.  “Soft-tissue anatomy of the primates: phylogenetic analyses based on the muscles of the head, neck, pectoral region and upper limb, with notes on the evolution of these muscles.”  Journal of Anatomy 219(3):273–359.  2011.  A family-tree study of primates built from 166 features of their head, neck, chest and arm muscles, using the authors' own dissections and the published literature.  The tree agrees with the molecular trees of primates, and the authors list the features that mark each branch.  The article relies on it for the claim that palmaris absence fits common descent.

1. 14a.

   Section Abstract:  “The most parsimonious tree obtained from the cladistic analysis of 166 characters taken from the head, neck, pectoral and upper limb musculature is fully congruent with the most recent evolutionary molecular tree of Primates.” ↩

2. 14b.

   Section Results, clade 19:  “Homininae (clade 19: Gorilla, Pan, Homo).”  “Palmaris longus is absent in > 5% of the cases [118:0→1].” ↩

3. 14c.

   Section Appendix 1, heading note:  “The Length (L), Consistency Index (CI) and Retention Index (RI) obtained for each character in the most parsimonious tree obtained from the heuristic analysis of the whole dataset (chars. 1–166) are given after the name of each respective character.” ↩

4. 14d.

   Section Appendix 1, character 118:  “118. Palmaris longus is absent in > 5% of the cases (L 1, CI 100, RI 100).”  “the palmaris longus is always, or almost always, present in the specimens of taxa of CS-0 [0], but it is absent in more than 5% of the cases in specimens of Gorilla, Pan and Homo [1].”  The same entry lists the muscle as present in the Rattus, Tupaia, Cynocephalus, Lemur, Propithecus, Loris, Nycticebus, Callithrix, Saimiri, Aotus, Pithecia, Macaca, Cercopithecus, Colobus, Papio and Hylobates specimens reported and dissected, and in one of two Tarsius. ↩ ↩ ↩ ↩ ↩ ↩

5. 14e.

   Section Appendix 1, character 118:  “In the Pongo specimens described by Church (1861–1862; one specimen)”.  “and dissected by us (two specimens) the muscle was present, and according to Loth (1931), Gibbs (1999) and Gibbs et al. (2002) it is present in all of the specimens of this genus”. ↩

6. 14f.

   Section Appendix 1, character 118:  “it is only present in seven out of 11 cases according to Keith's (1899) review, in 15% of the cases according to Loth's (1931) review, in four out of 11 cases according to Sarmiento's (1994) review, and in six out of 19 cases according to Gibbs' (1999) review (so it is clearly absent in more than 5% of gorilla limbs).” ↩

7. 14g.

   Section Appendix 1, character 118:  “it is only present in nine out of 12 cases according to Keith's (1899) review, in 95% of the cases according to Loth's (1931) review, in 15.5 out of 17 cases according to Sarmiento's (1994) review, and in 19 out of 28 cases according to Gibbs' (1999) review”. ↩

8. 14h.

   Section Appendix 1, character 118:  “Concerning modern humans, Loth (1931) stated that the muscle is present in about 97.5–98% of the cases, but in a more recent survey Gibbs (1999) stated that its incidence is said to range, within the recent literature, from 96.1 to 79.6%, with most authors referring to about 85% of the cases”. ↩

Sichting, Freddy et al.  “Evolutionary anatomy of the plantar aponeurosis in primates, including humans.”  Journal of Anatomy 237(1):85–104.  2020.  A review of earlier anatomists' descriptions of 40 primate species, mainly Loth's 1908 dissections of 126 primate feet, rather than new dissections.  It estimates each ancestor's likely state statistically and puts the plantaris running into the sole in the ancestor of all primates, but attached to the heel bone in the ancestor of Old World monkeys and apes.  The article uses it to date the move to the heel.

1. 15a.

   Section Introduction:  “In various mammalian taxa, the plantaris muscle is primitively continuous with the plantar aponeurosis (Lewis, 1962).”  “In its primitive mammalian form, its distal portion presents a fibrous cap as it passes smoothly over the posterior end of the calcaneal bone to enter the plantar sole and blend with the plantar aponeurosis”. ↩ ↩

2. 15b.

   Section Results 3.1:  “the plantaris muscle was absent in five species.  In nine species the plantaris muscle was present in a primitive state, smoothly passing beneath the calcaneal bone to blend with the plantar aponeurosis.  It was present but bound to or inserted into the calcaneal bone with limited or no further connection to the plantar aponeurosis in 26 species.” ↩

3. 15c.

   Section Results 3.1:  “it was absent in most suspensory species (state 0:5 of 13 species)”.  “almost all terrestrial species (88%) possessed plantaris muscles that are bound to or insert into the calcaneus (state 2).  The only exceptions were Gorilla (state 0) and Semnopithecus (state 1).”  In the paper's coding, state 0 means absent, state 1 means the muscle blends with the plantar aponeurosis, the tough sheet under the sole, and state 2 means it is bound to the heel bone. ↩

4. 15d.

   Section Results 3.1:  “The likelihood reconstruction (Figure 5a) for the plantaris muscle unambiguously predicts that the LCA of all primates most likely had a plantaris that blended with the plantar aponeurosis (state 1:94.0%).”  “The plantaris was most likely to insert into the calcaneus (state 2) for the catarrhine LCA (75.3%), the LCA of all apes (88.3%), great apes (79.7%), and African apes (83.1%).  Finally, the LCA of Pan and Homo probably had a plantaris that inserted into the calcaneus (state 2:98.0%).”  LCA means last common ancestor, the most recent ancestor of the named group.  The percentages are the authors' estimated likelihoods for each state. ↩ ↩ ↩ ↩

5. 15e.

   Table 1:  The table's notes f and g say:  “Presence of the plantaris muscle in chimpanzee is quite variable: 54.3% present (Loth, 1908).”  “Presence of the plantaris muscle in orangutan is quite variable: 3.7% present (Loth, 1908).” ↩

6. 15f.

   Section Discussion:  “However, among most extant catarrhines, the tendon of the plantaris is strongly bound to the periosteal tissue of the calcaneus, and therefore the plantaris loses its ability to directly increase tension in the plantar aponeurosis.” ↩

7. 15g.

   Section Discussion:  “In humans, the plantar aponeurosis is always present while the plantaris is missing in about 10% of humans (Daseler and Anson, 1943; Langdon, 1990).” ↩

8. 15h.

   Section Abstract:  “Ancestral state reconstructions suggest that the overall organization of the human plantar aponeurosis is shared with chimpanzees and that a similar anatomical configuration evolved independently in different primate clades as an adaptation to terrestrial locomotion.” ↩

Landfald, Ingrid C. et al.  “Plantaris tendon morphology in Papio anubis: a comparative anatomical study.”  Scientific Reports 16:26106.  2026.  A study of 46 lower limbs from 23 adult Anubis baboons, dissected and measured against a classification of human plantaris tendons.  Every limb had a plantaris, in one of two shapes: a band-like Type II (73.9%) or a sheet-like Type V (26.1%).  The authors warn that all 23 came from a single zoo-based population, and the article uses it to show that a baboon's plantaris also ends at the heel.

1. 16a.

   Section Abstract:  “This study examined plantaris tendon morphology in 46 lower limbs from 23 adult Anubis baboons (Papio anubis) using standardized dissection, morphometry and a human-derived insertional classification.  A plantaris muscle was present in all specimens”.  “Type II predominated (73.9%), whereas Type V occurred in 26.1% of limbs.” ↩

2. 16b.

   Section Results:  “Type II featured a relatively slender, cord-like tendon running along the medial border of the Achilles tendon and inserting into the medial region of the calcaneal tuberosity in close continuity with the Achilles tendon rather than as a completely independent structure.”  Type II is the band-like shape, and it was the more common of the two (73.9% of limbs). ↩ ↩

3. 16c.

   Section Discussion:  “it is consistent with the possibility that the plantaris apparatus in humans has undergone substantial reorganisation rather than simple reduction”.  The authors offer this as a possibility their baboon data fit, not as a result. ↩

Doyle, Shaun.  “'Selfish gene' theory, the ENCODE project and 'vestigial' muscles.”  Creation Ministries International.  Sep 2007.  A feedback reply by Shaun Doyle, assistant editor of the Journal of Creation, to a first-year medicine student's email about selfish gene theory, junk DNA, the palmaris longus and genetic variation.  It is an email answer, not a study.  On the palmaris it argues that people were created with the muscle and that some have since lost it through mutation.  The article calls it the creationist reply that goes furthest on the palmaris, and uses it for the homology point.

1. 17a.

   Section Reply, on the palmaris longus:  “There are a number of possible functions for the palmaris longus.”  “Its variability would be attributable to the fact that people can cope without it.  Thus, it is likely that all people were created with it and it could have been more crucial in a pre-technological age, i.e. grasping spears and other implements.  Mutational loss probably accounts for why some don't have it.  Such mutations would not be heavily selected against in a post-industrial age.” ↩ ↩ ↩

Mitchell, Elizabeth.  “Are 'Vestigial Organs' Really 'Proof of Evolution . . . on Your Body'?”  Answers in Genesis.  Mar 31, 2016.  An Answers in Genesis article that replies to a 2016 YouTube video from Vox on vestigial organs.  It answers the video's examples one at a time, and for the palmaris longus it argues that a structure can be done without and still not be a vestige of evolution.  The article uses it as the creationist reply on the palmaris longus and on the loss of structures.

1. 18a.

   Section Palmaris Longus Muscle:  “The palmaris longus, according to many reports, is quite unnecessary, its absence presumably causing no difference in grip strength.  And being long, strong, and dispensable, this "vestigial" structure is a favorite among surgeons who harvest it for tendon grafts.  But we must point out that the fact that a structure can be done without does not mean it is a footprint—a vestige —of an evolutionary past.  Such a claim presumes we evolved from animals; it does not prove that we did.” ↩

2. 18b.

   Section Palmaris Longus Muscle:  “A 2012 study published in the journal Physiotherapy reports that high-performance athletes in sports requiring a strong grip were substantially more likely to have a palmaris longus than athletes performing at a lower level.” ↩

3. 18c.

   Section Palmaris Longus Muscle:  “A 2010 study published in Clinical Anatomy compared the strength of this motion in the two hands of people who had only one palmaris longus.  Regardless of which hand was dominant, strength was significantly greater in the hand with a palmaris longus.” ↩

4. 18d.

   Later section, on loss.  “However, whenever a structure or a function is, over time, lost within a particular kind of animal, or among humans, there has been either a lack of expression or a loss of information.  Such a loss in no way demonstrates that an evolutionary gain of information once happened in the deep past.” ↩

Chauhan, R.  “Atypical Innervation Of Palmaris Longus: A Case Report.”  Journal of the Anatomical Society of India 52(2):171–173.  2003.  A case report from 2003 by an anatomist at the All India Institute of Medical Sciences in New Delhi, who dissected one adult male cadaver and found a second nerve branch to the palmaris, reaching its tendon and the palmar aponeurosis.  The author warns that surgeons who take the palmaris as a graft could damage that branch.  The article uses it because it repeats the wording of McGrouther's 1996 textbook section, that the main function of the palmaris is to anchor the skin of the palm.

1. 19a.

   Page 172:  “These post operative complications in the donor can be avoided if palmaris longus is used as a graft as loss of this tendon results in no major abnormality of hand function.  But Mc Grouther (1996) states that the main function of palmaris longus is to anchor the skin and fascia of hand and hence to prevent degloving of palmar skin from horizontal shearing forces.”  Page 173:  Reference 17 in the list gives the source as:  “Mc Grouther, D.A. Gray's anatomy In: Muscle. 38th Edn; Churchill Livingstone Edinburgh. p 846. (1996).” ↩

Fowlie, Craig et al.  “Assessment of the presence/absence of the palmaris longus muscle in different sports, and elite and non-elite sport populations.”  Physiotherapy 98(2):138–142.  2012.  A cross-sectional survey of six hundred and forty-two medical students, sports club members and national athletes, who filled in a questionnaire about their sport and were checked for the muscle with a standard test.  In sports that need a cylindrical grip, elite athletes had the muscle more often than non-elite athletes, and players of sustained-grip sports had it more often than players of other sports.  The article uses it as its main athletic evidence, which it calls suggestive and small.

1. 20a.

   Section Abstract:  “Six hundred and forty-two medical students, members of sports clubs and national athletes.”  “The presence of the palmaris longus was higher in elite athletes (21/22, 96%) than non-elite athletes (66/84, 79%; P=0.066) for sports that require a dominant-handed or two-handed cylindrical grip (18/22, 82% and 19/35, 54%, respectively; P=0.034).  For both elite and non-elite athletes, the presence of the palmaris longus was higher in those participating in sustained grip sports (325/387, 84%) compared with sports that do not require a sustained grip (150/197, 76%; P=0.012).” ↩

Dimitriou Ioannis et al.  “Palmaris Longus Muscle's Prevalence in Different Nations and Interesting Anatomical Variations: Review of the Literature.”  Journal of Clinical Medicine Research 7(11):825–830.  2015.  A review of 32 published studies that measured how often the palmaris longus is absent, with a table of each study's country, sample and rate.  It finds absence ranging from 1.5% to 63.9%, and says the muscle varies more than any other muscle in the human body.  The article uses its range and its country figures, and the journal later printed a correction to it.

1. 21a.

   Section Abstract:  “The prevalence of the palmaris longus (PL) muscle varies more than any other muscle in the human body.  Its absence across the world ranges between 1.5% and 63.9%.” ↩

2. 21b.

   Section Discussion:  “The lowest absence was observed in Zimbabwe (1.5%) with unilateral and bilateral agenesis being 0.9% and 0.6%, respectively”.  “The highest prevalence of PL muscle absence was observed in Turkey in 1997 by Ceyhan and Mavt that noticed the remarkable percentage of 63.9% of absence”. ↩

3. 21c.

   Section Discussion, table 1:  Rows as printed (author, country, sample, absence): Gangata 2009, Zimbabwe, 890, 1.5%; Ceyhan and Mavt 1997, Turkey, 7,000, 63.9%; Hiz 2011, Turkey, 1,000, 15%; Kose et al. 2009, Turkey, 1,350, 26.6%; Eric et al. 2010, Serbia, 800, 37.5%. ↩

4. 21d.

   Section Discussion:  “There have been 21 studies that examined the laterality in the PL muscle absence.  Bilateral agenesis of the PL muscle was more common in nine studies”.  “unilateral agenesis was more common in four studies”.  “eight studies noted that unilateral and bilateral absence of the PL muscle had no statistical difference”. ↩

Throckmorton, Zach et al.  “Non-adaptive evolution of the m. palmaris longus in the Homininae.”  bioRxiv.  Feb 17, 2015.  A preprint, posted before peer review, by three authors at an osteopathic medical college, which collects human counts of the muscle's absence and dissection records from chimpanzees, gorillas and orangutans.  It finds that absence varies widely between human populations, and suggests the muscle may be drifting without selection in the African apes and humans.  Its text and tables disagree in places (13 orangutans in the text, 16 in Table 2; 15 of 21 gorillas lacking the muscle in the text, 13 of 19 scored in the table rows), and the article uses it for the apes and for the claim that removing the muscle does no harm.

1. 22a.

   Section Abstract:  “different populations of humans exhibit remarkable variation in the frequency of palmaris longus agenesis, from less than 5% of Chinese to nearly 65% of Indians.”  “Comparative dissection-derived data reveal substantial variation in palmaris longus agenesis (PLA) in populations of extant humans (H. sapiens), chimpanzees (Pan spp.), and gorillas (Gorilla spp.) - but not orangutans (Pongo spp.), which apparently always develop this muscle.” ↩

2. 22b.

   Table 1:  Row "Thompson et al. (1921)": N 1,201; bilateral presence 908; unilateral absence 113; bilateral absence 180; European-American.  Row "Ceyhan & Mavt (1997)": N 7,000; ancestry given as "Indian". ↩

3. 22c.

   Paragraph 3:  “Absence of the palmaris longus muscle has not been shown to significantly affect grip or pinch strength (Sebastin et al. 2005, Ertem et al. 2007).  Its tendon is often harvested for grafts”.  “Adverse effects suffered by patients resulting from the surgical removal and relocation of their palmaris longus have not been documented.  Therefore, its absence likely does not affect fitness in humans.” ↩

4. 22d.

   Paragraph 5:  “There are no systematic, large-sample surveys of muscular variation in the great apes.”  “Though only 13 orangutans are noted for this character in the literature, palmaris longus was present in all 26 of their arms.  Of the 61 chimpanzees surveyed and reported by researchers, six exhibited bilateral palmaris longus agenesis and seven exhibited unilateral PLA; that is, approximately one out five of chimpanzees lack palmaris longus in at least one arm.  Gorillas exhibit the highest rates of great ape PLA, with 15 of 21 specimens lacking this muscle in one or both antebrachia.” ↩

5. 22e.

   Paragraph 6:  “This selection pressure is diminished in more terrestrial apes and humans; that is, negative selection against individuals lacking palmaris longus is relaxed in the African apes and humans.”  “Released from its role in arboreal locomotion, m. palmaris longus could potentially be undergoing non-adaptive evolution (i.e., drift) in the Homininae.  Though our data are not a direct test of this assertion, they are consistent with it.” ↩

6. 22f.

   Paragraph 7:  “the wide range of human subpopulation PLA frequency variation casts doubt on such a simple interpretation of the data.  Some human subpopulations exhibit palmaris longus agenesis frequency like chimpanzees, while others more closely match gorillas.” ↩

Soltani, Ali M. et al.  “The Variation in the Absence of the Palmaris Longus in a Multiethnic Population of the United States: An Epidemiological Study.”  Plastic Surgery International 2012:282959.  2012.  A prospective study of 516 patients at two hand clinics in Los Angeles, tested for the muscle with Schaeffer's test, in which the patient joins the thumb to the little finger while flexing the wrist.  It found the muscle absent in 14.9% of white non-Hispanic patients, 13.1% of white Hispanic patients, 4.5% of African American patients and 2.9% of Asian patients.  The article uses it for the differences by ancestry, and for its account of why surgeons take the tendon.

1. 23a.

   Section Abstract:  “Ethnically, there was no difference between white (non-Hispanic) and white (Hispanic) patients, with prevalence of 14.9% and 13.1%, respectively.  However, African American (4.5%) and Asian (2.9%) patients had significantly fewer absences of the PL than the Caucasian, Hispanic reference group”.  Section Methods:  516 patients; Schaeffer's test.  “confirmed by an attending hand surgeon.” ↩

2. 23b.

   Section Introduction:  “most studies have shown that absence of the PL is not associated with any significant physical or functional deficits, and therefore, the PL is frequently harvested for use in many different hand, reconstructive, and orthopedic surgeries”.  “The PL has a characteristically short belly and long tendon, making it an ideal donor for tendon grafts”. ↩

Pękala, Przemysław A. et al.  “Congenital absence of the palmaris longus muscle: A meta-analysis comparing cadaveric and functional studies.”  Journal of Plastic, Reconstructive & Aesthetic Surgery 70(12):1715–1724.  2017.  A systematic review with two separate meta-analyses of palmaris absence, one pooling cadaver dissections and one pooling clinical tests on living people.  Clinical tests reported absence more often, which matters here because the 20% pooled rate cited above comes from clinical studies and may count some thin tendons as missing.

1. 24a.

   Section Abstract:  “Our main findings revealed that the absence of PLM is more frequently reported in functional studies.  Moreover, functional tests likely overestimated the absence of PLM and recommend future studies to assess the validity of functional tests and use an imaging assessment prior to excluding the use of a palmaris longus tendon graft in patients in whom a function test identified the absence of PLM.” ↩ ↩

Aversi-Ferreira, Roqueline A. G. M. F. et al.  “Morphometric and Statistical Analysis of the Palmaris Longus Muscle in Human and Non-Human Primates.”  BioMed Research International 2014:178906.  2014.  A small comparison of the palmaris longus, a forearm muscle, in 14 human cadavers and in monkeys, lemurs and apes, measuring the muscle belly against its tendon.  The non-human samples are very small, its ape samples being one newborn orangutan and two young chimpanzees, and the Discussion contradicts itself in places.  The article uses it for how the muscle's shape and tendon length change across primates.

1. 25a.

   Section Results:  “the palmaris longus tendon presented an aspect similar to pennate in all Lemuriformes and New World primates (Figure 1), but fusiform to Macaca fuscata (unique exemplar of Old World primates) and to apes (Pongo sp. and Pan sp.) and modern humans.”  “Shorter tendons were observed in Lemuriformes and longer in modern humans (P < 0.05, Figure 2).” ↩ ↩

2. 25b.

   Section Conclusions:  “Apparently, in primates, the PL tendon relative size seems to increase from ancestors genera to more derived ones.  This suggests that this muscle is weaker in terrestrial primates when compared to arboreal primates.” ↩

3. 25c.

   Section Discussion:  The authors are repeating an older claim, not testing it themselves.  “Indeed, it is reasonable to suggest that PL is a degenerative muscle because, according to Meglioli [21], its agenesis is associated with a recessive gene.” ↩

van Sterkenburg, M. N. et al.  “The plantaris tendon and a potential role in mid-portion Achilles tendinopathy: an observational anatomical study.”  Journal of Anatomy 218(3):336–341.  2011.  An anatomical study that dissected one-hundred and seven lower extremities to see how the plantaris tendon joins the Achilles tendon.  In 11 legs (10%) the two were firmly joined in the middle of the Achilles tendon, where Achilles pain usually sits.  The authors say clinical and histological studies are needed to confirm the role of the plantaris tendon in that pain.  The article uses it for the link between the plantaris and Achilles pain.

1. 26a.

   Section Abstract:  “One-hundred and seven lower extremities were dissected.”  “In all specimens a plantaris tendon was identified.  Nine different sites of insertion were found, mostly medial and fan-shaped onto the calcaneus.  In 11 specimens (10%) firm connections were found at the level of the calcaneal tendon mid-portion.” ↩ ↩

Peck, David et al.  “A comparison of spindle concentrations in large and small muscles acting in parallel combinations.”  Journal of Morphology 180(3):243–252.  1984.  A 1984 laboratory study that measured the stretch sensors called spindles in dog muscles and combined those figures with published human ones.  In every group of small and large muscles examined, the small muscles had the higher spindle density.  The article uses it because Menton's sensory argument for the plantaris rests on it.

1. 27a.

   Section Abstract:  “A small short muscle frequently acts across a joint in parallel with a vastly larger and longer muscle; therefore it should play a minimal role in the mechanical control of that joint.”  “Data existing in the literature were used to ascertain spindle densities in human PMCs controlling joints in the cervico-occipital region and the extremities.”  “In all PMCs examined, the spindle density of the small muscles was significantly higher than that of their large counterparts.  It is therefore proposed that the small muscles of PMCs may function as "kinesiological monitors" generating important proprioceptive feedback to the central nervous system.” ↩ ↩

Wen, Jimmy et al.  “Achilles Tendon Scraping With Plantaris Tendon Removal for Achilles Tendinopathy: A Systematic Review and Meta-analysis.”  Foot & Ankle Orthopaedics 10(2).  2025.  A systematic review and meta-analysis of seven studies of 235 patients, in which surgeons scraped the Achilles tendon and removed the plantaris tendon at the same time.  The authors say the findings should be read cautiously, because the evidence is limited and the studies differ widely.  The article uses it to show that surgeons now remove the plantaris as treatment.

1. 28a.

   Section Abstract, Results:  “Seven studies including 235 patients (291 tendons) with a mean age of 40.8 years (27.2-52) and a mean follow-up time of 23.2 months (6-69.6) were analyzed.”  “RTA (1 study) and RTS (4 studies) were 100% and 95.5%.”  “The complication and revision rates were 11 (3.8%) and 5 (1.7%), respectively.” ↩

2. 28b.

   Section Abstract, Conclusion:  “These findings should be interpreted cautiously given the limited available evidence and high study heterogeneity.” ↩

Sanders, Lita.  “Badly designed arguments: 'vestigial organs' revisited.”  Creation Ministries International.  Nov 25, 2011.  A reply from Creation Ministries International, a creationist ministry, to a reader's list of supposedly useless human organs, answered one at a time.  It is the ministry's own reply, not a study.  The article uses it for the creationist answers on the palmaris and the plantaris.

1. 29a.

   Section Entry "Palmaris (longus) muscle":  “While this muscle is highly variable, and its absence (in around 10% of the population—most frequently in Caucasian people but less frequently in other populations) isn't associated with a measurable loss in grip strength, the fact that it isn't badly atrophied in the people who possess it indicates that it has some use.” ↩

2. 29b.

   Section Entry "Plantaris muscle":  “The plantaris has an unusual number of proprioceptive receptor end organs, so it probably plays a role in proprioception.  And it does weakly aid in plantarflexion of the ankle joint and flexing of the knee joint.” ↩