93 



The second part of the temporal muscle has the usual origin and 

 insertion. 



The superficial temporal weighs , . 6 oz, 



The true temporal, . ....... 16-J oz. 



The vertical fibres of the masseter close the jaw directly without 

 producing any pressure on the joint ; hut the fan-shaped jibres of this 

 muscle cause a powerful pressure on the condyle of the lower jaw, 

 forcing it backwards into its socket. Such seems to be also the function 

 of the superficial fibres of the temporal muscle, which press the condyle 

 into its socket, as well as close the mouth. This pressure seems to be 

 necessary, in consequence of the habit the Lion has of carrying his prey 

 in his mouth for a long time before he devours it ; for the weight so car- 

 ried would inevitably dislocate the jaw, if there were not a special pro- 

 vision made in the action of the masticating muscles to guard against it. 



3. MM. pterygoidei. 



The first part of these (externus) weighs . | oz. 



Its origin is the posterior portion of the pterygoid plate, and it is 

 inserted into the masseter muscle at the angle of the jaw. Its action 

 is to draw the fibres of the masseter forward, and give them a longer 

 leverage. 



The second portion of the pterygoid muscle (internus) weighs 2 oz. 



It arises from the anterior portion of the pterygoid plate, with an 

 extensive origin also from the floor of the orbit, and is inserted two 

 inches from the angle of the jaw. 



Its action is to close the jaw, and draw it forward. 



4. M. digastricus, oz. 



This is the proper muscle for opening the mouth in all the car- 

 nivora. 



Its origin is the mastoid process. 



Its insertion is into a line 3 \ inches in length backwards from the 

 symphysis of the jaw, along the mylo-hyoid ridge. 



The Eev. Samuel Haughton, M. D., Fellow of Trinity College, Dub- 

 lin, read the following Paper :— 



Notes on Animal Mechanics. 



No. Y. — The Muscular Anatomy oe the Seal.* 



The muscular anatomy of the Seal differs in many important particu- 

 lars from that of the other Carnivores ; and this difference seems to be 

 occasioned principally by its aquatic habits, which render it better 

 adapted for locomotion in the water than on dry land. In the anterior 



* The drawings from which the woodcuts were made were taken from nature by my 



son. 



