DISSECTION OP THE HEAD AND NECK. 189 



THE PTERYGO-MAXILLARY REGION AND THE REGION OP THE 

 GUTTURAL POUCH. 



Directions. — The outer surface of the inferior maxilla having been 

 laid bare from the condyle to the symphysis by the removal of the 

 muscles, the dissector is to make two sections with the saw. The first 

 is to be made obliquely from a point about an inch above the last 

 molar tooth to the angle of the jaw ; the second, close above the 

 symphysis. In making the sections, the edge of the saw must be kept 

 parallel to the surface of the bone, in order to avoid injury to the sub- 

 jacent structures. The jaw is next to be disarticulated by inserting a 

 strong scalpel into the joint ; and the scalpel is also to be passed round 

 the coronoid process, which will be felt embedded in the temporal 

 muscle, in the temporal fossa. The vertical ramus is now to be entirely 

 removed, at the same time leaving in position the parts beneath it. 

 This is to be done by raising the bone at the angle, and cutting the 

 muscular fibres inserted into its deep face. The edge of the knife is to 

 be kept cutting on the bone, which is at the same time to be forcibly 

 tilted upwards and forwards until the coronoid process is torn out of 

 the temporal muscle. The horizontal ramus is next to be folded down- 

 wards and outwards ; and, to permit this, it is only necessary to cut and 

 raise slightly the mucous membrane below the molar teeth. When these 

 operations have been effected the dissection will take the form of Plate 

 30. The vertical ramus is to be retained to show the insertion of the 

 pterygoid and temporal muscles. 



The External Pterygoid Muscle (Plate .30) is conical in form, with 

 the apex below. Its fibres arise from the outer surface of the sphenoid 

 bone above the entrance to the subsphenoidal canal, and from the entire 

 outer surface of the subsphenoidal process. They pass upwards and 

 backwards to be inserted into the inner aspect of the neck, or constric- 

 tion, below the condyle of the lower jaw. 



Action. — When the right and left muscles act simultaneously the 

 lower incisors are made to protrude in front of the upper. When the 

 muscles of one side act singly the entire inferior maxilla is thrown to 

 the opposite side ; and by the alternate contraction of the two muscles 

 the triturating action of the jaws and teeth is produced. 



The Internal Pterygoid (Plate 30) is a much more powerful muscle 

 than the preceding, from which it is separated by the inferior dental 

 nerve and vessels. It occupies a position on the inside of the vertical 

 ramus analogous to that of the masseter on the outside, the ramus 

 being included between the two muscles. Its fibres arise from the 

 bony crest formed by the subsphenoidal process and the palatine bone, 

 and they pass backwards to be inserted into the depressed inner surface 

 of the vertical ramus. 



