274 PRIMATES order x 



jugal. The lachrymal bone, as well as the lachrymal foramen, lies within the 

 anterior margin of the orbit. The facial bones are only moderately elongated, 

 are sometimes veiy short, and ascend abruptly backward. The nasal bones 

 are short ; the narial aperture is directed forward and is bounded above by 

 the nasals, laterally and below by the premaxillaries. The frontals are 

 anchylosed into a single bone ; the large parietal bones meet at the sagittal 

 suture and only exceptionally form a parietal crest. As a rule, the supra- 

 orbital ridge is also but slightly developed. The mandible has a horizontal 

 inferior margin, a high and usually broad ascending branch, and an obliquely 

 inclined chin, in which the two anteriorly converging branches are co-ossified. 



In front of the generally robust conical canine above, and posterior to it 

 below, the dentition is interrupted by a small diastema. The stoutness of 

 the canine is greater in the male than in the female. Only two chisel-shaped 

 incisor teeth are constantly present on each side above and below. In all 

 Old World apes, the superior molars have four, directly or obliquely opposite, 

 obtuse, conical or angular tubercles, the hypocone being sometimes weaker than 

 the protocone. In American apes, the protocone is sometimes entirely absent. 

 The inferior molars have but two pairs of tubercles, which often are united 

 by thin transverse ridges, yet frequently remain quite distinct. The third 

 molar is characterised by an additional cusp on the posterior margin. The 

 premolars above and below consist of a usually pointed external cusp and 

 a stout but low internal tubercle. In the Old World apes there are two 

 premolars present on each side above and below, but in the New World 

 forms there are three premolars. In the milk dentition, the posterior cheek 

 teeth are like the first true molar. 



The vertebral column consists of seven cervical, eleven to fourteen dorsal, 

 four to seven lumbar, five sacral, and an extremely variable number of caudal 

 vertebrae. The individual vertebrae, as well as the remaining bones of the 

 skeleton, agree essentially with those of man. In many South American 

 apes, the tail attains three times the length of the body ; in the Old World 

 Simiidae, it is completely absent. The relative length of the anterior and 

 posterior extremities varies extremely. In the CercopWiecidae, both are of 

 moderate and approximately equal length ; in Hi/lobates and Ateles, they are 

 much elongated, while in most Simiidae, the anterior extremities are 

 considerably longer than those behind. The humerus often has an entepi- 

 condylar foramen. The radius and ulna are separate, stout, and can be 

 twisted round each other. The carpus is short and broad ; its posterior 

 border articulating with the forearm forms a convex curve ; the carpals are all 

 distinct, and, except in the Chimpanzee and Gorilla, a rather large centrale is 

 present. The trapezium has a saddle-like articular surface for the opposable 

 thumb, which, however, is frequently represented merely by a short vestige 

 of the metacarpal, and is less movable than in man. The phalanges are 

 convex on the dorsal side and flat on the planter surface, the last phalanx 

 being reduced distally, flattened and scarcely curved. The slender femur 

 lacks a third trochanter ; the tibia and fibula are well developed and touch 

 each other only at their extremities. The astragalus has a convex, unfur- 

 rowed, tibial articular surface, and a lateral facet for articulation with the 

 fibula. The calcaneum has a long tuberosity and is distinctly truncate 

 below. The short but stout hallux is always opposable ; hence the pes is 

 fitted to assume the function of a hand. 



