Dissection of Sheep^s Head. 223 



surface being marked in the centre by double crescent-shaped 

 ridges of enamel, so disposed as to present along with the 

 central mass of dentine, and external crust of cement, alter- 

 nate layers of hardened tissue, having different degrees of 

 density: the complexity in question being the result of peculiar 

 plications of the formative capsule, some of which are longitu- 

 dinal, or project inward from the sides of the capsule, and form 

 peninsular folds of enamel upon the grinding surface of the 

 tooth, whilst others depend vertically from the summit of the 

 matrix into the body of the tooth, and form islands of enamel 

 when the crown begins to be wornf ; and, lastly, that the 

 last true Molar of the lower jaw presents the character found 

 in all E/uminants, viz., a third, posterior, lobe. 



Dissection of Digastric and Mylo-Hyoid Muscles, and 

 Mylo-Hyoid Nerve. By the removal of the jaw as described 

 above, the Student will be enabled to investigate from the 

 side the relative positions of the muscles, nerves, ducts, and 

 vessels : and will first note that the main bulk of the muscle 

 that was removed along the inferior margin of the jaw was 

 the anterior belly of the Digastric muscle ; next that the 

 more fleshy and massive muscle scraped away from the inner 

 surface of the angle of the jaw was the insertion of the 

 Pterygoid ; and lastly, will observe the cut end of the Dental 

 nerve where it was cut across in removing the jaw. 



He should now dissect close along the internal aspect of 

 the Pterygoid (being especially careful not to injure any of 

 the delicate nervous structures near its anterior margin) ; and 

 then turn it upwards, with a view to exposing the posterior 

 inch of the duct of the Submaxillary Gland, and the tendon 

 of the Digastric Muscle. Then dissect the long anterior 

 belly of the Digastric away from the edge of the mouth, 

 leaving in situ the muscle that lies internal to it, and whose 



t Owen. 



