146 SKELETON. 



The Ploughshare, (Vomer.) 



This single bone is placed between the nostrils, and forms a 

 considerable part of their septum. It is frequently more in- 

 clined to one side than to the other. It is formed of two laminae, 

 between which there is a very thin diploic structure. 



The sides of the vomer are smooth and parallel. It has four 

 margins. The superior is the broadest, and has a furrow in it 

 for receiving the azygous process of the sphenoid bone. The 

 anterior margin being directed obliquely downwards and for- 

 wards, its front half joins the cartilaginous septum of the nose, 

 and the posterior half receives, in a narrow groove, the nasal 

 plate of the ethmoid. 



The posterior margin of the vomer is smooth and rounded, 

 making the partition of the nostrils behind. The inferior mar- 

 gin articulates with the spine or ridge of the superior maxillary 

 and palate bones, which exist at their internal border. 



(Lower Jaw, Os Maxillare Inferius, Maxittaire Inferieur.) 



This bone forms the lower boundary of the face, and is the 

 only one in the head capable of motion. In early life, its two 

 halves are separable, being joined at the middle line only by 

 cartilage; but, in the course of two or three years after birth, 

 they are consolidated, and the original cartilage disappears, 



It consists of a body or region which corresponds with the 

 teeth, and two extremities or branches. 



The inferior part of the body presents a thick and rounded 

 edge, which is the base. The upper part of the body is formed 

 by the alveolar cavities for receiving the teeth. The line of 

 union between the halves, being called the symphysis, is marked 

 in front by an elevated ridge, terminated below by the ante- 

 rior mental tubercle a triangular rising. In many subjects 

 this tubercle is bounded on each side by a rounded prominence 

 of bone, which gives to the forepart of the jaw an unusual 

 squareness in the living subject. Just above the latter promi- 

 nence, there is, on each side, a transverse depression, from 

 which arises the levator muscle of the lower lip. On a line 

 with this depression, and removed a little distance from its ex- 



