SPECIAL ANATOMY. 125 



pterygoid bone and tlie crus of the sphenoid, and becomes 

 inserted into the internal surface of the neck of the inferior 

 maxillary condyle. The upper extremity of the inferior 

 maxilla should now be removed by disarticulation of the 

 joint, and sweeping a knife around the coracoid process 

 in the temporal fossa. It will be thus shown that a con- 

 siderable amount of fat assists in filling up this fossa, 

 thus allowing play of the coracoid process. Deficiency of 

 this fat causes that depression above the eyes noticeable 

 in old or emaciated horses. In addition we also see in this 

 fossa the 



Temporalis, a muscle which passes from its attachment 

 to the superior bony boundary of the temporal fossa, ex- 

 tending as far as the parietal ridges to become inserted 

 into the inner surface of the coracoid process of the inferior 

 maxilla. It is sometimes composed of two distinct parts, 

 and serves when acting alternately with its fellow to 

 give the jaw the lateral motion necessary for the grinding 

 of the food ; when acting in conjunction with its fellow it 

 aids in closing the mouth. 



Muscles which close the mouth : — Masseter externus, 

 masseter internus, temporalis, pterygoideus. We have 

 now exposed the posterior part of the orbit, which in the 

 horse consists of fibrous membrane, the periorhitale ; below 

 this is the internal maxillary artery. Commencing at 

 the termination of the external carotid, at the inner sur- 

 face of the temporo -maxillary articulation, this vessel 

 takes a direct course towards the sphenoideal foramen, 

 and having passed through it gains foramen rotundum, 

 and thus becomes again visible just below the orbit. It 

 takes a straight course towards the maxillary hiatus, where 

 it breaks up into three branches which adopt the names of 

 the foramina of the hiatus through which they pass. 

 Before arriving at the sphenoideal foramen this artery gives 

 of£ deep temporal branches upwards and branches doivn- 

 wards to masseter internus. Also the inferior maxillary 

 artery which passes through the posterior maxillary fora- 

 men, and courses with the corresponding nerve between 

 the plates of the inferior maxilla supplying the lower teeth, 

 and sending a small branch outwards through foramen 

 menti. In its course below the orbit the internal maxil- 

 lary artery gives off branches upiuards to the temporal 

 muscle, and ocular branches, which run to the eyeball and 



