SKELETON OF QUADRUMANA. 517 



metapopKyses which support them in the preceding caudals 

 continue to be developed to near the end of the tail. The 

 diapophyses are single on each side in the seven anterior 

 caudals, but are divided into an anterior and posterior portion 

 on each side of the vertebrae throughout the rest of the tail. 

 The third to the sixth cervical vertebrae inclusive show an 

 anterior concavity and a posterior convexity of the articular ends 

 of the centrums in the transverse direction, an anterior convexity 

 and posterior conca\'ity in the vertical direction, producing an 

 interlocking joint, combining strength with freedom of motion, 

 and analogous to that in the neck of birds. The pleurapophysial 

 part of each transverse process is a broad depressed plate, with its 

 anterior margin j^roduced, and progressively increasing in size 

 from the third to the sixth vertebra. A similar increase is pre- 

 sented by the neural spines, especially in the sixth vertebra. As 

 in the Capuchins, the transverse process of the atlas of the 

 Spider-monkeys is perforated lengthwise only by the vertebral 

 artery, which afterwards perforates the neural arch. The atlas 

 has a hypapophysial ridge, and the axis shoAvs a corresponding 

 tubercle. Nine pairs of ribs articulate directly with the sternum, 

 which consists of eight bones and an ensiform cartilage. 



The vertebral column of the Platyrrhine Quadriimana is the 

 seat of greater and more important varieties : the caudal por- 

 tion is reduced to a stunted * coccyx,' the lumbar region is 

 shortened and strengthened, and the sternum is composed of 

 fewer and broader bones in the Apes properly so called. In the 

 Monkeys and Baboons, the dorso-lumbar vertebrae are nineteen 

 in number as a rule, either D 13, L 6, or D 12, L 7. The latter is 

 the common formula in the Macacques : the caudals varying from 

 upwards of 20 in Macacus radiatus to 15 in M. rhesus, and being 

 reduced to 3 or 4 in M. inuus. In the Baboons ( Cynocephalus), 

 the caudals also vary from 25 in C. porcarhis to 10 very small 

 and stunted vertebras in the Mandril ( C papio, fig. 344). In this, 

 as in the Black-faced Drill ( C. porcarius) and Thoth ( C. Thotli), 

 the dorso-lumbar vertebrae are reduced to D 12, L 6. An an- 

 apophysial tubercle is developed from the diapophysis of each 

 dorsal vertebra, increasing in length to the two last, in which it 

 has an independent origin. The metapophysis is suddenly de- 

 veloped from the tentli dorsal, and presents an articular surface 

 to a second facet on the outer side of the hinder zygapophysis of 

 the vertebra in front. The anapophyscs continue to be developed 

 from all the lumbar vertebrae, progressively decreasing as these 

 approach the sacrum, and appearing in the last as a mere ridge 



