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 
vertebre are less developed than in Man, and are more uniform in size. 
It will be noticed that whilst the lumbar vertebree 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 vertebree 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, as 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. 3 
The thorax, which is formed by seven true and six false ribs, is 
larger and more conical in form than in Man. The great activity of 
the Gibbons requires large respiratory organs; hence we find the 
thorax proportionally large (see Prof. Owen on Orangs, wbi 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 vertebre given 
above will show that the number of ribs varies considerably in the 
genus Hylobates. 
Section I]].—Or tur Fore Extremirizs. 
The clavicles, which from their great length throw the scapule 
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. 
