THE CHIMPANZEES AND ORANGS. 107 
In the Gorilla the sacrum (Pl. XXXVI. figs. 1 & 2) departs in a great and instructive 
degree from the Human type: it consists normally of five anchylosed vertebre, 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, ns) 
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 vertebre, 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 vertebrz, the 
confluent spines form a lower ridge with projections corresponding to the three upper 
vertebrz, of which the third prominence is the thickest, and there it ceases: the sacro- 
iliac symphysis is restricted to the first and second vertebre 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 vertebra. 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 male Australian, figured in Pl. XXXVI. figs. 5 & 6, consists, as in the 
Human species generally, of five anchylosed vertebre. They differ from the sacral ver- 
tebre 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. “Ihe two anterior sacrals and a 
small part of the third form the sacro-iliac joint. The neural arch of the last two sacra? 
vertebrze 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 (pl) ; 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, d) 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 vertebra. 
In the Anthropoid Apes, as in Man, the tail is reduced to three more or less stunted 
R2 
