36 OUTLINES OF EQUINE ANATOMY. 



canalis infra orbitale, a special chanuel of the "bone which 

 runs through the maxillary sinus) emerges with an accom- • 

 panying artery, both run forwards concealed from view by 

 levator labii superioris alseque nasi. From the point of 

 junction of the malar, lachrymal, and superior maxillary 

 bones, nasalis longus labii superioris arises. A considerable 

 portion of the inner surface of this bone is occupied in 

 forming the outer wall of the nasal chamber. Along the 

 central line extending from before backwards is a ridge to 

 which the inferior turbinated bone is attached. At about 

 the centre of the bone this terminates in bifurcating, form- 

 ing two lines, one of which runs upwards and backwards, 

 the other downwards and backwards, mapping out that 

 portion of bone which forms the inferior maxillary sinus. 

 The extreme inferior margin affords attachment to the 

 gums of the roof of the mouth ; higher up is a groove 

 running forwards for the palatine artery, and above this a 

 horizontal process, palatine process, projects inwards. It 

 extends neither as far as the anterior nor as the posterior 

 extremity of the bone, but anteriorly, gradually diminishes 

 in size to terminate imperceptibly ; posteriorly presents a 

 squamous surface extending on to the small part of the 

 tuberosity for union with the palate bone. This surface 

 presents a smooth groove, which helps to form the palatine 

 canal. The free margin presents numerous spiculse of bone, 

 which serve to keep it closely in apposition with the palatine 

 process of its fellow, and the two together form a groove 

 into which the anterior part of the inferior margin of the 

 vomer fits. The iij)per surface of this process helps to form 

 the floor of the nasal chamber, the inferior surface is 

 covered by the mucous membrane of the hard palate, with 

 its rich venous plexus. This bone assists in forming the 

 superior maxillary sinus through which two bony canals 

 pass, the canalis infra orbitale, and the bony covering of the 

 ductus ad nasum. 



OS LACHRYMALE forms the antero -internal part of 

 the orbit, assisting in forming its margin, thus being bent 

 upon itself in such a manner as to present two plates, 

 separated by the concave marginal border, which is for tbe 

 most part smooth, but centrally rather rough. The exter- 

 nal surface, therefore, as a whole, is convex, but it consists 

 of two concave plates. The anterior is the facial plate. It 

 presents at about its centre a tubercle (lachrymal) to which 



