The Skull of the Maixatus 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 
