THE HEAD. 63 



concave transversely, and elongated from before to beliind. The petrous portion has a consider- 

 able tympanic bulb upplied closely to the auditory canal, whicli is large and oblique bthiud. 

 The mastoid process is a simple crest situated above the auditory canal ; the hyoid prolongation 

 is absent. 



Bones of the Face. 



The face is much more extensive than the cranium in the majority of the 

 domesticated animals, and is composed of two jaivs — a bony apparatus that serves 

 as a support to the passive organs of mastication — the teeth. The superior or 

 anterior jaw, traversed in its entire length by the nasal cavities, is formed by 

 nineteen flat bones, only one of which, the vomer, is a single bone. The pairs 

 are : the supmHor and intermaxiUaries (or premaxillaries), the palate^ pterygoid, 

 malar, lachrymal, nasal, and superior and inferior turbinated hones. Of these 

 only four — the maxillaries — are intended for the implantation of the teeth ; the 

 others form the union between the cranium and the superior maxilla, or concur 

 in the formation of the nasal cavities. The lower jaw has for its base a single 

 bone — the inferior maxilla, or maxillary bone. 



1. Superior Maxillary Bone (Fig. 26). 



This bone, also named the super maxillary bone, the most extensive in the 

 upper jaw, is situated on the side of the face, and is bordered above by the 

 frontal, palate, zygomatic, and lachrymal bones ; below, by the premaxillary 

 bones ; in front, by the nasal bone ; behind and within, by that of the opposite 

 side. It is elongated vertically, is irregularly triangular, and exhibits two faces, 

 two borders, and two extremities. 



Faces. — The external face, which is more convex in the young than the old 

 animal, presents : 1. On the level of the fourth and fifth molar teeth, a vertically 

 elongated ridge which is continued above with the inferior border of the 

 zygomatic bone ; this is the maxillary spine. 2. The inferior orifice of the 

 tnaxillo-dental canal, or infra-orbital foramen. 



The internal face concurs in forming the external parietes of the nasal cavities. 

 "We observe, above and in front, a deep, wide, and diverticulated excavation, 

 forming part of the maxillary sinus ; above and behind, a surface roughened by 

 fine lamellie and denticulatious to correspond with the palate bone, and traversed 

 from above to below by a fissure which forms, in uniting with a similar fissure in 

 the latter bone, the palatine canal. For the remainder of its extent it is unequally 

 smooth, covered by the membrane of the nose, and divided into two surfaces by 

 a slightly vertical and sinuous crest that affords attachment to the maxillary 

 turbinated bone : the anterior surface, which responds to the middle meatus of 

 the nasal fossa, shows the lower orifice of the osseous lachrymal canal continued 

 by a fissure to the lower extremity of the bone ; the posterior surface belongs to 

 the inferior meatus. From this face is detached, near its inferior border, a wide 

 and long vertical plate, which forms, in Man and short-faced animals, a simple 

 process — the palatine process. This plate, uniting in the middle line with that on 

 the opposite side, concurs in forming the greater portion of the palatine arch. It 

 shows : an anterior slightly concave face, forming the floor of the nasal fossfe ; a 

 posterior face, buccal, furrowed by small fissures, perforated by fine openings, and 

 traversed along its length by a somewhat wide groove — the pctlatine fissure, which 

 commences above at the lower orifice of the palatine canal ; a denticulated border 



