Dissection of Sheep^s Head. 233 



which is the Superior Constrictor Muscle ; and next will scrape 

 away from the anterior margin of the ramus the attachment 

 of another muscle, viz. the anterior and larger belly of the 

 external pterygoid muscle. The object of the removal of the 

 section of zygomatic arch is now apparent, viz. in order to 

 admit of the extraction of the coronoid process of the jaw, 

 which is next to be drawn outwards through the gap made, and 

 turned over backwards ; access being by this means gained 

 for the examination of the second and shorter belly of the 

 external pterygoid muscle which is attached to the under 

 side of the internal angular prominence of the condyle of the 

 jaw. 



The External Pterygoid muscles are thus seen to occupy 

 the major part of the zygomatic fossa: they arise by two 

 heads placed close together, occupying a considerable area on 

 the Sphenoid, Pterygoid, and posterior aspect of the Superior 

 Maxillary bones. The fibres from both heads are marked 

 with tendinous intersections, and have a general downward 

 direction. When the muscles of both sides act together, the 

 lower jaw is slightly drawn forward ; but when the muscles 

 of one side act alone, the result is the advancement of one 

 condyle only, and hence the lateral motion of the jaw, throw- 

 ing the teeth to the side opposite to that on which the muscles 

 act. This action repeated alternately on both sides induces a 

 lateral grinding movement of the lower teeth. 



The inferior dental nerve should be removed from the 

 dental foramen in the jaw, and left (as to its upper course) in 

 situ, together with the mylo-hyoid branch which lies just 

 posterior to it, and which will be, later on, traced back to the 

 motor root of the inferior maxillary nerve : the buccal nerve 

 should also be traced up, and cleaned. In laying bare these 

 nerves towards the temporo-maxillary articulation, a large 

 vessel will be noted crossing them at right angles ; this is the 

 internal maxillary or deep Facial artery y the larger of the two 



H H 



