32 ANATOMY OF THE HORSE. 



Division — Into three surfaces, three angles, a basiform and an 

 apiform extremity. 



Surfaces. The internal or facial sui'face'i's. divided into two 

 portions by the zygomatic angle or spine : the upper division is 

 smooth and nearly flat, with the exception of a depression ante- 

 riorly, which marks the attachment of the nasalis longus labii 

 superioris ; the lower part is narrow, and roughened by the ad- 

 herence of the masseter. From this surface, posteriorly, arises 

 the zygomatic process, which is very obliquely sloped off, and 

 laminated for adaptation to the process of the same name, meeting 

 it from the temporal bone, the two together forming the zygomatic 

 arch. The internal or maxillary suface is concave, to enlarge the 

 capacity of the maxillary sinus, to which it contributes. The 

 orbital surface presents a smooth concavity, which forms the 

 infero-external part of the orbit, and is separated from the facial 

 surface by the orbital angle. 



Angles. The inferior angle constitutes the principal part of 

 the zygomatic spine : it is continuous with the temporal bone be- 

 hind, and in front by the superior maxillary. Tlie superior angle 

 is lunated, and constitutes the infero-external portion of the orbital 

 circumference. The posterior angle, or rather border, is jagged 

 and irregular, and unites with the superior maxillary bone. 



Extremities. The anterior extremity or base is broad, irre- 

 gular, and denticulated, and articulates with the superior maxillary 

 and lachrymal bones. The posterior or apiform end forms the 

 zygomatic process. 



Particularities. These bones contribute to the formation of the 

 orbits, maxillary sinuses, and zygomatic arches ; and their articu- 

 lations exhibit a sort of dove-tail mechanism. 



Connection — With the temporal, superior maxillary, and lachry- 

 mal bones. 



LACHRYMAL BONES. (OSSA LA CH RYM ALI A.) 



Situation. Antero-external part of the orbit. 



Form — Irregularly infundibuliform. 



Division — Into three surfaces and five borders. 



Surfaces. The external or facial surface, triangular, flattened, 

 and smooth, is bounded, laterally, by the external and internal 

 facial borders ; superiorly, by the orbital ridge. It exhibits, a 

 little above its centre, a rounded eminence, the lachrymal tubercle, 

 to which is fixed the orbicularis palpebrarum. — The internal sur- 

 face is concave, but very irregularly so, being divided into two 

 hollows by a cylindrical prominence, caused by the lachrymal 

 conduit. It constitutes part of the roof of the maxillary sinus. 



