182 DISSECTION OF THE DOG 



dissection the termination of the mandibular nerve, with its inferior 

 alveolar, lingual, and mylo-hyoid branches, will be displayed from the 

 inside. At the same time the dissector will note a part of the internal 

 maxillary artery and its inferior alveolar branch. 



M. pterygoideus externtts. — The external pterygoid muscle, much 

 smaller than the internal muscle of the same name, takes origin from a fossa 

 on the lateral face of the pterygoid and palatine bones, and is inserted into a 

 rough area on the medial surface of the mandible ventral to the condyloid 

 process. 



Dissection. — Remove as much as possible of the zygomatic bone without 

 injuring the orbit, and open up the infraorbital canal. The full extent 

 of the zygomatic gland will be exposed. 



Glandtjla zygomatica. — The distinctly lobulated zygomatic gland lies 

 under cover of the oral end of the zygomatic arch. Its deep face is in contact 

 with the pterygoid muscles, the periorbita, the internal maxillary artery, and 

 the maxillary nerve. The main duct of the gland is of some size and opens into 

 the mouth near the last molar tooth. In addition, there are generally several 

 smaller but inconstant ducts. 



The gland must be removed in order to allow of the examination of the 

 internal maxillary artery and the maxillary nerve. 



A. maxillaris interna. — As previously stated, the passage of the internal 

 maxillary artery through the alar canal permits of its division into two parts. 

 That part of the vessel which occurs before its entrance into the canal has 

 already been examined. The second part, that is to say the part after the 

 artery has traversed the canal, now falls to be discussed. 



From the oral end of the canal the internal maxillary artery pursues a 

 course over the surface of the pterygoid muscles in company with the maxillary 

 nerve. The temporal muscle and the zygomatic gland form its lateral relations. 

 Having arrived close to the entrance to the infraorbital canal, the vessel 

 divides into the infraorbital artery and a common stem from which the spheno- 

 palatine and greater palatine arteries arise. 



The following branches leave the second part of the internal maxillary 

 artery : (1) The ophthalmic artery (a. ophthalmica) leaves the parent vessel 

 immediately this emerges from the alar canal. A short length of the artery 

 may now be disclosed between the temporal muscle and the periorbita, but its 

 further examination should be deferred. (2) The buccinator artery (a. buccina- 

 toria) accompanies the buccinator nerve across the pterygoid muscles towards 

 the last molar tooth, and ends in the component parts of the cheek. (3) The 

 lesser palatine artery (a. palatina minor) crosses the pterygoid muscle, to which 

 it supplies one or more branches, and ends in the soft palate. Small twigs 

 also go to the hard palate. (4) The infraorbital artery (a. infraorbitalis) 



