The Skull of the Manatus Senegalensis and Manatee. 263 



row at first where they bound the upper part of the tem- 

 poral fossae, but gradually spread out into thick, broad, tri- 

 angular-shaped orbital plates, convex above and concave 

 beneath, to form the roof of the orbital chambers. These 

 orbital plates are larger than in the African skull. The 

 premaxillary bones are 7 inches in length, and extend back- 

 wards at the inner edge of the orbital plates of the frontal 

 bone for about 2 inches in the skull from Old Calabar ; the 

 premaxillaries are much smaller, less deflected in front, and 

 terminate behind at the anterior part of the frontal bone. 

 The distance from the incisive edge of the premaxillaries 

 to the fore part of the orbital cavities is 5 inches, or an inch 

 less than in the African skull. The orbital cavities are 

 larger and more rounded in the Honduras skull than in 

 that from Old Calabar. The length of the zygomatic pro- 

 cess is 5 inches, or half an inch less than in the African 

 skull ; it is also much less massive, more curved and concave 

 below. The glenoid surface is more elevated, with two 

 deep depressions at the under and back part, which are 

 but very slightly marked in the African skull. The malar 

 bone is 6J inches in length, and extends from the outer 

 edge of the glenoid ridge to the anterior part of the orbit. 

 It has a narrow zygomatic process behind, which gradually 

 expands into a broad vertical maxillary process, which ter- 

 minates in a twisted curved horizontal orbital plate, to form 

 the outer part of the floor of the orbital cavity ; and this 

 orbital plate rests on a similar curved orbital process of the 

 superior maxillary bone. The inner part of the floor of the 

 orbits is formed by a bridge-like process of the orbital plates 

 of the superior maxillary bones, which extends outwards 

 from the alveolar processes of the upper jaw. There is a 

 large infra orbital foramen, about an inch in diameter, 

 opening directly in front. The anterior nasal aperture is 

 considerably larger in the American than in the African 

 skull, although the extreme length and breadth of both is 

 almost the same. In the African skull the aperture is con- 

 tracted from side to side, both before and behind ; and as 

 the nasal fossa is narrower, shallower, and altogether less 

 capacious, the size of the anterior nasal aperture appears 



