184 DISSECTION OF THE DOG 



an elongated object of greyish colour connected by fine filaments with the 

 spheno-palatine nerve. The Vidian nerve of the pterygoid canal joins the 

 aboral extremity of the ganglion. 



N. mandibtjxaris. — The opportunity should now be seized to again examine 

 the mandibular nerve — the most ventral division of the fifth cerebral nerve — ■ 

 as it leaves the cranium by the oval foramen and lies alongside the first part of 

 the internal maxillary artery, ventral to the mandibular joint and lateral to the 

 pterygoid muscles. The various branches of the nerve are the deep temporal, 

 the masseteric, the buccinator, the superficial temporal, the pterygoid, the 

 lingual, the inferior alveolar, and the mylo-hyoid nerves, all of which have 

 been described as the dissection proceeded. 



Ganglion oticttm. — Close to the foramen ovale, the small otic ganglion 

 lies on the mandibular nerve, -with which it is connected by fine filaments. A 

 small bundle of fibres forms a link between the ganglion and the tympanic 

 nerve. 



The orbit and its contents now claim the attention of the dissector. The 

 bony boundaries of the orbit of the dog are very imperfect, the medial wall 

 alone being represented in the macerated skull. Of such bony wall as exists 

 the frontal bone forms by far the greater part. The lachrymal bone assists, 

 as does also a narrow strip of the palatine above the crest limiting the depression 

 from which the pterygoid muscles have their origin. Moreover, the entrance to 

 the orbit from the face is not completely encircled by bone. Only some three- 

 fourths of it is formed by the frontal, lachrymal, and zygomatic bones. The 

 rest is completed by the orbital band, a strong fibrous cord bridging the gap 

 between the rudimentary zygomatic process of the frontal and a small projection 

 on the zygomatic bone. 



Periorbita. — An exact definition of the orbit is produced by the stout, 

 conical, fibrous periorbita, the apex of which is adherent to the bone in the 

 neighbourhood of the optic foramen, while the base is fused with the orbital 

 band and the periosteum of the bony orbital margin. The periorbita, there- 

 fore, forms a definite separation between the orbit and the temporal and 

 pterygo-palatine fossae, and contains the eyeball and its various accessory 

 structures. 



The axis of the orbital cavity is not parallel to the long axis of the head ; 

 nor are the two orbital axes parallel to each other. Each axis runs in a dorsal, 

 lateral, and oral direction from the optic foramen. 



Dissection. — In order to effect a proper exposure of the contents of the orbit 

 it is necessary to remove the coronoid process of the mandible and the 

 temporal muscle attached thereto. For convenience the orbital band and 

 as much as possible of the periorbita should also be taken away. In the 

 removal of the periorbita care must be exercised not to injure the structures 

 lying close to its deep face. 



