FACE 



143 



an air-cavity which opens into an ethmoidal meatus. The inner plate curves 

 inward and unites with the vomer and ethmoid to form a horizontal plate (Lamina 

 transversalis), which divides the posterior part of the nasal cavity into an upper 

 olfactory part and a lower respiratory part. 



The pterygoid bone is nearly vertical in direction, and is narrow in its middle, 

 wide at eacli end. The external surface is free below and forms the inner wall of 

 the pterygoid fossa. The lower end is notched and forms a distinct hamulus. 



The nasal bone is very long and its width is almost uniform, except at the 

 anterior end, which is pointed and reaches almost as far forward as the premaxilla. 

 The facial surface is flattened from side to side. In profile it is nearly straight in 

 some subjects, variably concave in others. The external l)order is free to a small 

 extent in front only; otherwise it is firmly connected with the premaxilla and 

 maxilla. In the adult the frontal sinus extends into the posterior part of the bone. 



The lacrimal bone is very sharply bent. Its facial surface presents a deep 

 depression, surmounted l)y a ridge or tubercle. On or close to the orbital margin 

 are two lacrimal foramina which lead to the lacrimal canals. The orbital surface 

 presents a fossa in which the inferior ol)lique muscle of the eyeball arises, and its 

 lower part bears a crest, which is crossed obliquely by a vascular furrow\ The 

 upper border articulates with the frontal only. The bone concurs in the formation 

 of the maxillary sinus. 



The malar bone is strongly compressed from side to side. Its facial surface 

 is small and presents a fossa which is continuous with the depressions of the maxilla 

 and lacrimal. The orbital surface is still smaller and is smooth and deeply grooved. 

 The zygomatic process is very extensive, especially in the vertical direction. Its 

 external surface is convex and free, and bears a rough eminence in its middle. Its 

 internal surface is concave; it is overlapped in front by the maxilla, and in the 

 remainder of its extent is free and smooth. The upper border is thick and rounded 

 in front, where it forms the lower part of the orbital margin; behind this it forms 

 an extensive notch which receives the zygomatic process of the temporal. (It 

 might be regarded as dividing into frontal and temporal branches.) The lower 

 border is convex and becomes thinner behind. 



The turbinal bones resemble those of the ox. The superior turbinal is, however, 

 relatively longer, less fragile, and more firmly attached to the nasal bone. There 

 is no middle turbinal. 



The vomer is very long. The anterior extremity reaches to the body of the pre- 

 maxilla or very close to it. The lower border is received into a groove formed by 

 the nasal crest of the maxilla and palate bones and in front by the palatine processes 

 of the premaxillse. The posterior border is concave, thin, and sharp. 



The OS rostri (or prenasal bone) is situated in the snout between the nostrils. 

 It has the form of a short three-sided prism. The upper surface is convex and is 

 notched at each end. The lateral surfaces are concave, smooth, and converge 

 below, forming a grooved lower border. The posterior surface is triangular, 

 notched centrally, and rough laterally. The anterior surface is deeply pitted and 

 is surrounded by an irregular sharp border. 



The mandible is very strong, and differs very much from that of the horse or 

 ox. The body narrows decidedly in front; the lingual surface is deeply concave; 

 the mental surface is strongly convex, slopes downward and backward, and forms 

 a distinct prominence at the point of divergence of the rami. Above this promi- 

 nence is a pair of foramina. The alveolar border presents six alveoli for the in- 

 cisor teeth, and a little further back two large cavities for the canine teeth. There 

 are two pairs of mental foramina of considerable size and a variable number of 

 smaller ones. The rami diverge more than in the horse or ox, and the upper part 

 is somewhat incurved. The horizontal part is very thick and strong. Its outer 

 surface is strongly convex from above downward. The inner surface is prominent 



