466 THE ANATOMY OF VEETEBEATED ANIMALS. 



it is reduced to a small metacarpal (to which, usually, a single 

 miuute nodular phalanx is articulated), and is completely 

 hidden beneath the integument. The pelvis is, generally, 

 elongated, and the anterior ramus o£ the pubis lies at right 

 angles with the long axis of the narrow ilium. The tuber- 

 osities of the ischia are everted, but not rugose. In Ateles, 

 the pelvis is broader, and the pubis forms a more open 

 angle with the ilium. The calcaneal process is always very 

 short, and compressed from side to side. 



The brain- case is rounded and devoid of strong crests. 

 There is no distinct mastoid process, and the styloid is not 

 ossified. The coronal suture is generally V-shaped, the 

 apex of the frontal bone extending far back on the vertex 

 of the skull. The alisphenoid and the parietal bones unite 

 upon the side walls of the skull. The external auditory 

 meatus is not ossified, the tympanic bone retaining its foetal 

 hoop-like form. The frontal bones approach one another 

 on the floor of the skull, but rarely unite over the junction 

 of the presphenoid with the ethmoid. On the inner sur- 

 face of the periotic bone there is a fossa overarched by the 

 anterior vertical semicircular canal, in which the flocculus 

 rests. In Ateles the greater part of the tentorium is ossified. 

 In other respects, the skull presents extraordinary variations 

 among the Plafyrrhini ; the two extremes being presented by 

 the Howling Monkeys (Mycetes) and the SquiiTcl Monkeys 

 (Chrysothrix). In the former, the face is very large and 

 prominent, with a low facial angle. The roof of the brain- 

 case is depressed; the plane of the occipital foramen is 

 almost perpendicular to the basi-cranial axis ; and that 

 of the tentorium is very much inclined. The occipital 

 condyles are, consequently, situated at the posterior end 

 of the iads cranii, and the basi-cranial axis is as long as 

 the cerebral cavity. In Chrysothrix, on the contrary, the 

 face is relatively small, with a high facial angle; the 

 brain-case is moderately arched; the plane of the ten- 

 torium is horizontal, like that of the occipital foramen, 

 which lies but little behind the middle of the base of the 

 skull. The basi-cranial axis is much shorter than the 



