38 OUTLINES OF EQUINE ANATOMY. 



anterior and external boundary of tlie posterior naris in 

 the skeleton. Its free extremity unites with its fellow ante- 

 riorly at a symphysis, and thus the two bones form a 

 ''■ jpalatine arcli,'^ to which, in the fresh subject, the fibrous 

 layer of the fixed portion of the soft palate is attached. 

 The free margin of the ridge on the inner surface of the 

 bone is united to the vomer, and by the groove of that bone 

 separated from its fellow. The external margin of the 

 palatine process is convex, and presents a serrated edge for 

 union with the palatine process of the superior maxilla. 

 Posteriorly this roughened surface increases in size, pre- 

 senting a very wide squamous surface for union with the 

 inner surface of the tuberosity of the superior maxilla. 

 This surface is rough in all parts except at a central 

 groove running forwards, which combines with a similar 

 depression on the maxillary surface to form the palatine 

 canal. Behind this the bone is smooth ; it is over here the 

 superior maxillary division of the sixth nerve and the 

 internal maxillary artery course in their way from the 

 sphenoidal to the maxillary hiatus. The extreme posterior 

 part of the inferior margin articulates with the crus of os 

 sphenoides, assisting to form the pterygoid ridge, to the 

 superior part of the internal surface of which is attached 

 the pterygoid bone. 



OS PTERYGOIDEUM is a small plate of bone attached 

 to the under surface of the cranium at its junction with the 

 face ; consists of two parts, the anterior of which is flattened 

 from side to side, the posterior from above downwards 

 and is the widest and thinnest. The anterior iorms a small 

 tuberous prominence, attached to the inner surface of the 

 palatine bone, curved slightly outwards at its extremity, 

 thus producing a groove through which tensor palati plays 

 (bound down by the pterygoid ligament) . The superior sur- 

 face of the posterior part articulates with ossa sphenoides 

 and palati, and its inner margin meets the vomer. To its 

 under surface masseter internus and pterygoideus gain 

 either direct or indirect attachment. 



OS ZYGOMATICUM OR THE MALAR BONE forms the 

 major portion of the outer boundary of the orbit. It is 

 pyramidal, presenting three surfaces, three margins, a base 

 and an apex. The external surface is for the most part 

 convex, anteriorly it is flat, affording attachment to 

 nasalis longus labii superioris. Its inferior margin is 



