36 ANATOMY OF THE HORSE. 



THE INFERIOR MAXILLARY BONE. 

 (OS MAXILLARE INFERIUS.) 



Constituting, by itself, the inferior maxilla, or lower jaw. 



Situation. — Composing the inferior and posterior parts of the 

 face. 



Form. — Symmetrical, bearing much resemblance to the letter 

 <1 ; the angular or narrow part being presented forwards, the sides 

 diverging and opening backwards. 



Division. — Into body, neck, sides, and limbs or branches, to- 

 gether with their respective external and internal surfaces and 

 borders. 



The body is the anterior undivided portion, reaching back so 

 fiir as to include the tusks within their sockets. The neck is the 

 contracted part springing from the body ; the two together form- 

 ing a solid bond of union between the sides, sustaining them, 

 together with the branches, in immovable relative position. I n the 

 young subject, a longitudinal median suture, named the inferior 

 maxillary symphysis, divides the bone at this part into separable 

 synniietrical halves; bony union, however, solidifies the two early 

 in life, after which they are no longer distinct pieces. The exter- 

 nal surface of the body is convex and rounded, and in places rough 

 and porous, from the attachment of the levator menti and gums. 

 A groove across the neck marks the course of the former symphy- 

 sis. At the place where the neck joins the side, near the supe- 

 rior border, is the anterior maxillary foramen, which forms the 

 outlet of a canal running between the laminai of the bone along 

 the roots of the molar teeth : it is traversed by the third division 

 of the fifth pair of nerves. The internal surface of the body is 

 slightly concave, and is rough and porous from the attachments 

 of the gums and membrane of the mouth; that of the neck forms 

 a channel for the tongue, and receives the insertion of the frcenum 

 linguis. 2'he border projects forward, forming a parabolic curve, 

 and presenting, superiorly, conical alveolar cavities for the six 

 lower incisive teeth and the two inferior tusks ; posteriorly, on the 

 neck, the border rises into a sharp edge, which is rendered less 

 prominent in old horses, in consequence, it would appear, of the 

 repeated pressure and friction of the bit. 



The sides are the parts comprehended between the neck and 

 the branches: they support all the inferior molar teeth. They in- 

 crease in breadth from before backward, are flattened laterally, 

 and present external and internal surfaces, superior and inferior 

 borders. The surfaces, though, generally speaking, they may be 

 jn'onounced to be flat, possess a degree of prominence in early and 

 adult life which they lose in age : this may be ascribed in part to 



