410 THE ANATOMY OF YERTEBRATED ANIMALS. 



the metacarpal bone of tlie pollex. That part of the tibialis 

 a7iticus which goes to the metatarsal of the hallux is usually 

 very distinct, and is sometimes reckoned as a separate muscle, 

 the abductor lo7igus hallucis. 



In the Gibbons and in the Orang, there is a complete set 

 of deep extensors for the four ulnar digits, the tendons of the 

 extensor indicis and extensor minhni (^z^i^*_ subdividing to 

 BujDply the third and fourth digits. 



In the Gorilla and Chimpanzee each of these muscles have 

 but a single tendon, as is the usual arrangement in Man. 



The interossei of the hand are each divided into two mus- 

 cles with distinct tendons — Oi flexor brevis 2JTi77ii intertiodii and 

 an exte?isor h^evis tertii hite^iiodii. The division is less obvi- 

 ous in the Orang than in the other Antliropomorpha. 



In Hylobates, the tendon of t\ie flexor perforans pedis goes 

 only to the fifth digit, and is not directly connected with that 

 of the flexor longus hallucis, which supplies the other four 

 digits. In the Orang, also, the tendons of the two muscles are 

 separate ; but ^q flexor perforans supplies the second and the 

 fifth digits, and the flexor hallucis tfie third and fourth. It 

 gives no tendon to the hallux. In both the Chimpanzee and 

 the Gorilla, a very large tendon is given to the hallux by the 

 flexor hallucis, and it also supplies the third and fourth digits. 

 The tendon of flexor longus digitorum is but slightly con- 

 nected with that of i\\e flexor hallucis, and its divisions go to 

 the second and fifth toes. In both the manus and the pes of 

 Hylobates a muscle occurs which is not, at present, known in 

 any other Mammal. It arises from the second metacarpal or 

 metatarsal bone, and is inserted by a long tendon into the pre- 

 axial side of the ungual phalanx of the second digit ; it may 

 be termed " abductor tertii internodii secundi digiti.''"' 



The Orang, in like manner, stands alone in possessing a 

 small but distinct opponens hallucis.^ 



The volume of the brain, in the Orang and in the Chim- 

 panzee, is about twenty-six or twenty-seven cubic inches ; or 

 about half the minimum size of a normal human brain. In the 

 Gorilla, the volume rises to near thirty-five cubic inches. In 

 the Gibbons the brain is very much smaller ; and the Siamang, 

 among these, is remarkable for the short posterior lobes of the 



* It must be "borne in mind that these statements respecting the myology 

 of the AnthropomorpJia are based upon my own dissections (sometimes suj)- 

 plemented by those of Duvernoy and other anatomists) of particular speci- 

 mens. Endless varieties will no doubt be met with by those who carry theii 

 inquiries further. 



