728 

 Genus Ateles. 







Dental formula : t ?=?, c {, i> g, m g=36. 



4687. The skeleton of the Marimonda or White-bodied Spider-Monkey (Ateles 

 Belsebuth}. 



The vertebral formula is : / cervical, 14 dorsal, 4 lumbar, 3 sacral, and 31 caudal. The 

 transverse process of the atlas is perforated lengthwise by the vertebral artery, which after- 

 wards perforates the neural arch : that of the fourth, fifth and sixth cervicals has a progress- 

 ively increasing pleurapophysial plate : that of the seventh consists of the diapophysis only, 

 and is imperforate. The atlas has a hypapophysial ridge, and the axis shows a corresponding 

 tubercle. The centrum of the succeeding cervicals is produced backwards into a convex form. 

 The tuberosity above the dorsal diapophyses becomes a ridge in the eleventh dorsal, which is 

 produced forwards into an angular metapophysis : in the thirteenth dorsal it is produced to 

 the same extent backward into an anapophysis : in the fourteenth dorsal these processes are 

 distinct and well-developed, but the diapophysis has disappeared. The anapophysis is de- 

 veloped from the first and second lumbar vertebrae, and the diapophysis from all the lumbars, 

 progressively increasing to the penultimate one. A pair of hypapophyses begin to be de- 

 veloped from the fifth caudal, and increase in size in the sixth and seventh. The haemal arch 

 is anchylosed to these processes in the eighth and ninth caudals, but the hypapophyses con- 

 tinue to be developed, without the addition of that arch, throughout the succeeding caudal 

 vertebrae. The anterior zygapophyses disappear in the ninth caudal, but the metapophyses 

 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 fourteenth pair of ribs is wanting in this skeleton : nine pairs of ribs articulate 

 directly with the sternum, which consists of eight bones and an ensiform cartilage. The long 

 and large coracoid has an angular tuberosity. The humerus is not perforated either above or 

 between the condyles. This bone, and, still more, the radius and ulna, are remarkable for 

 their length and slenderness, as are also the bones of the digits, with the exception of the 

 pollex, which is reduced to a rudiment of its metacarpus, and is concealed beneath the skin 

 in the recent animal. 



The femur, tibia and fibula, are also longer, but the tibia is not attenuated in the same 

 proportion. The thumb of the hind foot is complete and well-developed. The prehensile 

 tail compensates for the loss of that quality in the hand. 



Mus. Brookes. 



4688. The skeleton of the Yellow Spider-Monkey (Ateles arachnoides). 



The vertebral formula is : 7 cervical, 14 dorsal, 4 lumbar, 3 sacral, and 32 caudal. Four- 

 teen pairs of ribs are preserved. The left femur shows a united fracture, and is half an inch 

 shorter than the other. 



Mus. Brookes. 



