488 Zoological Society. 



processes of the atlas are produced long and narrow, more so than 

 in Man. The first dorsal vertebra is the smallest, after which they 

 gradually increase in size. The transverse processes of the lumbar 

 vertebrae are less developed than in Man, and are more uniform in size. 

 It will be noticed that whilst the lumbar vertebrae of the Chimpanzee 

 and Orang Utan are four, two of the Gibbons have five and one has 

 six ; in the extent of this region therefore they approach Man. The 

 sacral vertebrae are perfectly anchylosed together, but not to the 

 coccygeal, and form about their middle an angle, the lower part 

 being curved backwards. The upper portion thus remains in a line 

 with the vertebral column, and part only is thrown backwards instead 

 of the whole, us in Man. The first pair of foramina are almost obli- 

 terated, and are therefore not so large as in Man and the Chimpanzee ; 

 the three following are persistent. As in the Orangs, the sacrum is 

 narrower than in the human skeleton. The weakness of these parts 

 indicates the less amount of capability of assuming the erect posture 

 than is granted to Man. The Gibbons are especially fitted for arbo- 

 real progression ; and although by the assistance of their lengthened 

 fore extremities, touching the ground on either side, and as it were 

 acting as crutches, they are perhaps more at home in the erect pos- 

 ture on level surfaces than either the Chimpanzee or Orang Utan, 

 yet their movements are awkward and constrained. The Gibbons 

 are the only Mammals which can assume the erect posture whilst 

 they walk on all four extremities. 



The thorax, which is formed by seven true and six false ribs, is 

 larger and more conical in form than in IVIan. l^he great activity of 

 the Gibbons requires large respiratory organs ; hence we find the 

 thorax proportionally large (see Prof. Owen on Orangs, ubi supra) ; 

 at the same time it affords increased attachments to the strong pec- 

 toral muscles required by the lengthened arms. One contrivance 

 thus answers two ends. 



The last three ribs are unattached by cartilage to the sternum, 

 which consists of five pieces, whereof the last is free. In the num- 

 ber of its component pieces the sternum of the Active Gibbon agrees 

 with Man and the Chimpanzee, and differs from the Orang Utan, 

 where it is formed of seven or eight small pieces arranged in a double 

 row. The manubrium differs slightly from the human in being pro- 

 portionally broader. 



Compared with the ribs of the Chimpanzee, those of the Active 

 Gibbon are slight in form ; compared with those of a Baboon, they 

 are strong. 



A reference to the dorsal column of the table of vertebras given 

 above will show that the number of ribs varies considerably in the 

 genus Hylobates. 



Section III. — Of the Fore Extremities. 



The clavicles, which from their great length throw the scapulae 

 far backwards, and give great breadth to the shoulders, are flattened 

 horizontally, have but little marks of tendinous attachment, and pre- 

 sent neither the double curvature of Man nor the straightness of the 

 Orang Utan, but a simple gentle curvature outwards. 



