Zoological Society. 



487 



elongation of the palate ; by the small proportional size of the infra- 

 orbital foramen ; by the obliquity of the occipital plane, and by the 

 large size of the canine teeth ; by the elongation of the lower jaws, 

 in consequence of the length of the muzzle and palate ; by the in- 

 creased depth of the symphysis, and by the small size of the foramen 

 which gives exit to the blood-vessel nourishing the teeth and the 

 accompanying nerve. 



This skull agrees with that of the Chimpanzee in its smallness 

 proportionally to the body, in its generally elongated form, in its 

 anterior contraction, in the marks of the attachments of the temporal 

 muscles, in the large supraorbital ridges, in the obliquity of the plane 

 of the foramen magnum, and in the slight arch of the nasal bones. 



It differs from that of the Chimpanzee in the supraorbital ridges 

 not uniting, in the obliteration of the sutures, in the smaller size of 

 the infraorbital foramen and of the foramen of the dental blood-vessel. 

 The lower jaw is proportionally shallower. The cranium of the 

 young Chimpanzee is far broader, more arched and less anteriorly 

 compressed, and therefore far more anthropoid. These characters 

 however degenerate with age. 



It differs yet more from the form of skull exhibited by the adult 

 Orang Utan, where the strongly developed cranial ridges and widely 

 expanded zygomatic arches give the skull a carnivorous aspect. 

 These peculiarities we have seen to be absent in the Gibbon. The 

 flatness of the bones of the nose of this Ape is an additional distinc- 

 tion. On the other hand, it agrees with the Orang in the oblitera- 

 tion of the cranial sutures of the adult. 



In the large development of the supraciliary ridges this skull re- 

 minds us of the Baboons, which present however a more degraded 

 form, and may be distinguished by the greater narrowness of the 

 cranium, by the less circular form of the orbits, by the greater pro- 

 longation of the muzzle and the greater space between the zygomatic 

 arch and the skull. 



The dentition of the Gibbon claims no especial notice ; the in- 

 cisors and molars are moderate in size, whilst the canines are large, 

 their roots apparently reaching nearly to the internal corner of the 

 orbits. 



Section II. — Of the Trunk. 



The vertebral formula of the Agile Gibbon is — cervical, 7 ; dorsal, 

 1 3 ; lumbar, 5 ; sacral, 4 ; coccygeal, 4. The comparison of these 

 numbers with those of some of its congeners and near allies will be 

 exhibited by the following table : — 



Of the cervical vertebrae I need only remark, that the transverse 



