ANATOiMY 01- THE HORSE. 37 



the teeth, and in part to the comparative porousness or incompact- 

 ness of structure of the young bone. The external surface is occu- 

 pied by the depressor labii superioris ; the internal by the muscles 

 of the hyoidean region. The vacuity between the sides takes the 

 name of inter-maxillary space. — Of the borders^ the superior exhi- 

 bits twelve quadrangular alveolar cavities for the molar teeth, 

 formed by the separation of the laminae composing the bone, and 

 the addition of so many transverse thin partitions or septa. The 

 inferior border is thick, round, and smooth in early life ; but, as 

 age advances, grows thin, sharp, and irregular. 



The branches, the parts directed upwards, are broad, thin, 

 and slightly curved ; and ofl'er for notice two surfaces, two borders, 

 two processes, and a notch. The surfaces are generally smooth, 

 though they exhibit marks of muscular attachment : the external 

 one is clothed by the masseter ; the internal, by the pterygoideus 

 internus ; the latter, also, is pierced a little behind the last molar 

 tooth, by the posterior maxillary foramen, which forms the entrance 

 to the dental canal, the anterior maxillary hole being its outlet. 

 The borders : — The posterior is broad, and roughened by the attach- 

 ment of the stylo-maxillaris and masseter : the part where it 

 makes its curvature to join the side is called the angle of the jaw. 

 The anterior border is thin, and presents a sharp edge, turned 

 inwards : it gives attachment to the buccinator and depressor labii 

 infcrioris. Processes : — The posterior border is surmounted by the 

 condyle,^the transverse, cylindroid, smooth convexity which is 

 received into the glenoid cavity in the temporal bone. The ante- 

 rior border ends in the coronoid process, which is flattened on its 

 sides, has sharpened edges, and is slightly curved backwards : 

 into it is implanted the temporal muscle. Between the two pro- 

 cesses is the corono-condi/Ioid notch, which affords space for the 

 motion of the jaw, as also for the insertion of the temporal nmscle. 



HI.— THE HEAD IN GENERAL. 



We shall now take a review of the head in its entire or articu- 

 lated state, making, to facilitate the description, a 

 Division of it into External and Internal parts. 



The External Parts 

 maybe conveniently distinguished into superior, posterior, inferior, 

 and lateral surfaces ; and each of these surfaces admits of a fur- 

 ther subdivision into cranial and facial regions. 

 THE SUPERIOR EXTERNAL SURFACE comprehends— 

 1. The superior cranial region, in which we find 

 several zigzag denticulated lines, denominated sutures, indicating 

 the boundaries and articulations of the several individual bones. 



