186 THE GENERAL ANATOMY OF GORILLA [SECT. A 



The M. plantaris never appears to be developed in the Gorilla 

 as a separate muscle, although it is of common occurrence in the 

 Chimpanzee. The fascia plantaris is described by Sommer 1 as 

 being very strong. Loth 2 dissected the fascia in a Chimpanzee 

 and an Orang-utan and found the tibial component well developed, 

 though the fibular part was weak in comparison with the condition 

 presented by it in Cynocephali. 



The M. flexor accessorius digitorum (M. quadratus plantae) is 

 rare, though it has been found in Gorilla (its mode of insertion 

 in the Simiidae is also unlike that of Man, as it may in 

 Chimpanzees form an attachment to the tendons of the M. flexor 

 brevis digitorum). 



The tendons of the plantar aspect of the foot are arranged as 



f< >iiows. 



M. flexor brevis digitorum. This muscle shews a distinct 

 approach to the human condition, inasmuch as its superficial head 

 takes origin partly from the os calcis, and not only from the fascia 

 plantaris as in the lower Primates generally. This superficial part 

 provides (perforated) tendons for digits II and Hi (more rarely 

 li, HI and iv). 



The deep head of the muscle arises from the tendon of the 

 M. flexor longus digitorum, and provides perforated tendons for 

 digits iv and v, though the last-mentioned is often absent 3 . As 

 regards the long flexor muscles of the hallux and digits, Hepburn 4 

 found the Gorilla to be the anthropoid ape most nearly resembling 

 Man. The M. flexor longus hallucis contributes a strong slip of 

 tendon to that of the M. flexor longus digitorum. In regard to 

 all these plantar structures, the Orang-utan retains its distinction 

 as an aberrant form. 



The pedal interosseous muscles are grouped about the third 

 digit, and herein the Gorilla differs from Man and resembles the 

 Chimpanzee, the Orang-utan, some varieties of Gibbon, and the 

 Cercopithecidae generally: it must be admitted that many Gorillas 

 possess the human arrangement, these muscles being then grouped 

 about an axis formed by the second digit. In this respect the 



1 Jenaische Zeitxchrift, 1906. - op. cit. p. 135 zujxra. 



3 Sawalischin, Morphologisches Jahrbueh, Band xlii. Heft 4, with literature. 



* Cf. J. A. P., 1892. 



