552 ANATOMY OF VERTEBRATES. 



The orbits have a full oval form in the Orang ; thev are almost 

 circular in the Chimpanzee and Siamang, more nearly circular, and 

 Avith a more prominent rim, in the smaller Gibbons ; in the Gorilla 

 alone do they present the form which used to be deemed peculiar 

 to Man. The occipital foramen is nearer the back part of the 

 cranium, and its plane is more sloping, less horizontal in the 

 Siamang than in the Chimpanzee and Gorilla. Considering the less 

 relative prominence of the fore part of the jaws in the Siamang, 

 as compared with the Chimpanzee, the occipital character of that 

 Gibbon and of other species of Hi/lobates uiRrks well their inferior 

 position in the quadrumanous scale. The characteristics of the 

 limbs in Man are their near equality of length, but the lower limbs 

 are the lousiest. The arms in Man reach to below the middle of 

 the thigh ; in the Gorilla, fig. 346, they nearly attain the knee ; in 

 the Chimpanzee, fig. 345, they reach below the knee ; in the Orang 

 they reach the ankle ; in the Siamang, fig. 180, they reach the sole : 

 in most Gibbons the whole palm can be applied to the ground with- 

 out the trunk being bent forward beyond its naturally inclined 

 position on the legs. These gradational differences coincide with 

 other characters determining the relative proximity of the Apes 

 compared with Man. 



In the Gorilla, the humerus, though less long compared with 

 the ulna than in Man, is longer than in the Chimpanzee ; in the 

 Orang it is shorter than the ulna ; in the Siamang and other 

 Gibbons it is much shorter. The peculiar length of arm in those 

 ^ long-armed apes ' is chiefly due to the excessive length of the 

 antebrachial bones. 



The difference in the length of the upper limbs, as compared 

 with the trunk, is but little between Man and the Gorilla. The 

 elbow-joint in the Gorilla, as the arm hangs down, is opposite the 

 ' labrum ilii,' the wrist opposite the ^ tuber ischii ; ' it is rather 

 lower down in the Chimpanzee ; is opposite the knee-joint in the 

 Orang ; and opposite the ankle-joint in the Siamang. The iliac 

 bones are not so broad in proportion to their length in any ape as 

 in the Gorilla. In the Orang they are flat, or present a concavity 

 rather at the back than at the fore part. In the Siamang they are 

 not only flat, but are narrower and longer, resembling the iliac 

 bones of tailed monkeys and ordinary quadrupeds. 



The lower limbs, though characteristically short in the Gorilla, 

 are longer in proportion to the upper limbs, and also to the entire 

 trunk, than in the Chimpanzee : they are much longer in both pro- 

 portions and more robust than in the Orangs or Gibbons. But the 

 guiding points of comparison here are the heel and the hallux. 



