THE CHIMPANZEES AND ORANGS. 107 



In the Gorilla the sacrum (PI. XXXVI. figs. 1 & 2) departs in a great and instructive 

 degree from the Human type : it consists normally of five anchylosed vertebrae, but they 

 are longer and narrower than in Man, and present a minor degree of forward cur- 

 vature. The neural foramina (n) are much smaller, and the neural spines (fig. 2, n s) 

 are more developed : they coalesce to form a single strong bony ridge, extended over 

 and gradually subsiding on the last sacral vertebra, the neural arch of which is entire. 

 The articular surface of the body of the first sacral vertebra (fig. 2) is one-third smaller 

 than in Man (figs. 6 & 8) ; the zygapophyses {z) are smaller, but the metapophyses (m) 

 are present and well developed. The iliac articular surface extends to the upper half of 

 the third vertebra, is narrower than in Man, but owing to the greater length of the first 

 and second vertebrae, it is longer. The posterior outlets of the nervous canals are very 

 small, and the whole neural canal is much more contracted. 



In the sacrum of the Orang {Pithecus Wurmbii), which consists of five vertebrse, the 

 confluent spines form a lower ridge with projections corresponding to the three upper 

 vertebrae, of which the third prominence is the thickest, and there it ceases : the sacro- 

 iliac symphysis is restricted to the first and second vertebrae and a small part of the 

 third. The neural arch is unclosed in the last two vertebrae. The entire sacrum is 

 relatively shorter, and broader above than in the Gorilla. 



In the Chimpanzee (PI. XXXVI. figs. 3 & 4) the sacrum more resembles in its general 

 form and proportions that of the Gorilla ; it also consists of five vertebrae. The neural 

 arch (n) is complete in each, and the spinous process is developed from all but the last, 

 the four posterior spines being confluent. The metapophyses are developed from the 

 four anterior sacrals : the three anterior ones join the iliac bones. 



The sacrum of the maleAustralian, figured in PI. XXXVI. figs. 5 & 6, consists, as in the 

 Human species generally, of five anchylosed vertebrae. They diflfer from the sacral ver- 

 tebrae of the Gorilla and Chimpanzee by their greater breadth and by their anterior 

 concavity both lengthwise and transversely. The nervous foramina are relatively much 

 larger : the spinous processes are shorter and thicker. The two anterior sacrals and a 

 small part of the third form the sacro-iliac joint. The neural arch of the last two sacral 

 vertebrae is complete. 



The characteristic peculiarities of the first sacral vertebra in Man, e. g. the greater 

 relative capacity of the neural canal (n), the larger size, especially in the antero-posterior 

 direction, of the articular surface of the centrum (c) ; the greater length of the coalesced 

 pleurapophyses {pi) ; and the less length of the neural spine, are shown in figs. 8 and 6, 

 as contrasted with figs. 2 & 4. 



In both the Gorilla and Chimpanzee the diapophyses of the last sacral vertebra (figs. 

 1 & 3, s 5, rf) terminate in an obtuse angle divided by a notch from the side of the body 

 of the vertebra, down which they are continued lower in the Chimpanzee than in the 

 Gorilla. In Man they subside gradually upon the sides of the last sacral vertebrae. 



In the Anthropoid Apes, as in Man, the tail is reduced to three more or less stunted 



R 2 



