SKELETON OF QUADRUMANA. 515 



carinate. Besides the wide canals for the vertebral arteries in 

 the ^ transverse processes ' of the atlas, the neural arch is perfo- 

 rated above the base of that process on each side for the passage 

 of a nerve. 



In the short-tailed Indri {Lichanotus Indri\ the atlas has a 

 short hypapophysis, but no neural spine : the transverse process 

 is moderately long and broad, and is perforated lengthwise and 

 vertically by the vertebral artery, which afterwards pierces the 

 neural arch. The transverse process is perforated in all the 

 other cervical vertebras: the pleurapophysial portion of that of 

 the sixth forms a broad lamella directed downward and out- 

 ward. Each of these cervicals has its hypapophysial ridge and 

 neural spine, the latter moderately long and slightly increasing to 

 the seventh. The broad neural arch is fissured behind. The 

 spines of the dorsal vertebras are continued of equal length 

 throughout that region, and have the same direction. The dorsal 

 diapophyses support each a metapophysial tubercle, which aug- 

 ments as they diminish, and seems to take their place in the 

 eleventh and twelfth vertebrae, the ribs of which have no tubercle. 

 In the twelfth dorsal the metapophysis projects from above the 

 prozygapophysis, and is continued backward upon a well-deve- 

 loped anapophysis, which commences at once in that vertebra, 

 and continues to be developed, although decreasing in length, 

 to the penultimate lumbar inclusive. The metapophyses, which 

 are prominent in the anterior lumbar vertebra, gradually subside 

 as these approach the sacrum. The diapophysis has a low rough 

 tubercle on the first lumbar, which is developed into a depressed 

 plate increasing in length and breadth as the succeeding lumbars 

 approach the sacrum. As in the true Lemurs, eight pairs of ribs 

 directly join the sternum, which consists of seven bones and an 

 ensiform cartila2:e. 



Nineteen is the usual number of dorso-lumbar vertebra? in the 

 Platyrrhine group, the Spider-monkeys {Afeles) offering the ex- 

 ception of eighteen, viz. d u, l 4 : the varieties which have been 

 formulised in the type-genus Cebus are due to freedom or con- 

 fluence of pleurapophyses, as e.g. D 12, L 7, Cebus liijpoleucus\ 

 D 13, L 6, C capucinus ; D 14, L 5, in most Capuchins. The tail 

 is long in all, and prehensile in most Platyrrhines ; it rarely 

 has so few as 18 (^CalUthrix sciureus and C. Spixii), usually 

 30 vertebras, or upwards, as in Ateles iKiniscus, which has 33 

 caudals. 



In the little Ouistiti {Hapale Jacchus), the accessory tubercle 

 appears upon the middle dorsal vertebra ; it divides into met- and 



L L 2 



