422 DR. 0. F. SONN'TAG ON THE ANATOMY, 



run for a few paces in the erect posture. The maintenance of 

 the erect attitude in Man is eflected by a very complex and 

 beautifully adjusted nervous, muscular, and osseous mechanism ; 

 but many factors co-operate in the Chimpanzee to make it 

 quadrupedal when on the ground. In the first place, the centre 

 of gravity is high, for the greatest weight of the body is nearest 

 the arms, l^he animal will naturally hill to the ground unless 

 it uses its arms as supports. In Man, on the contrary, the 

 centre of gravity is low down near the supporting legs. As 

 distension of the abdomen by food and pregnancy throws the 

 line of gravity farther forwards in Man, the effect of similar 

 conditions on the Chimpanzee will make the arms all the more 

 necessary as supports. In the second place, the muscles of the 

 back are more rigid in the Chimpanzee, so they are not employed 

 as in Man for adjusting the Lalance to suit awkward positions. 

 Thirdly, the arrangement of the bones and joints of the pelvis 

 and lower limbs in the Chimpanzee is such that the lower limbs 

 cannot be converted into strong supporting pillars. Finally, the 

 muscles are not so subdivided as in Man, so the movements are 

 more massive. There is not the fine co-ordination of movements 

 which Man obtains through a highly organised brain, a delicate 

 and complex nervous mechanism, and a subdivided muscular 

 system, whose elements can group themselves to produce complex 

 actions. 



The Chimpanzee experiences joy and anger, and young 

 ones manifest jealousy if their companions are petted. It 

 expresses these emotions by grimaces instead of fine facial 

 expressions. The lips and cheeks exhibit gross movements, and 

 many teeth are exposed. The reasons for this are the coarseness 

 of the platysma and its very intimate union with the labial 

 muscles; and the latter are coarse, fused, and devoid of fine 

 subdivisions. 



The muscles of mastication are built on the same plan as in 

 Man, but they are more powerful. And the prognathism makes 

 the levatores and tensores palati more horizontal than in Man. 



The columns of the erector spinae are coarser than in Man, and 

 pass farther up into the neck. And the shortness of the neck 

 almost obliterates the sub-occipital triangle. 



The muscles attached to the shoulder girdle are so arranged 

 that the arm can be moved far backwards. In addition to the 

 usual elevators, which are more powerful than in Man, there is a 

 levator claviculse. The nerve supply to the rhomboideus, levator 

 scapulae, and first part of the serratus magnus is very lich. The 

 Chimpanzee has also a dorso-epitroehlearis. 



If several animals are examined it is seen how the pectoralis 

 minor writes its evolutionary history. 



There is considerable fusion between the muscular bellies of 

 the flexors and extensors of the wrist and fingers. The flexor 

 carpi ulnaris is more bulky than in Man, and it is inserted into a 



