384 -^^ VISON. [Vol. XI. 



its respective side. At a distance of one-JiftJi of the circumfer- 

 ence fro77i the dorsal line, a cleavage into two -membranes takes 

 place, one of which descends almost vertically through the body- 

 wall to the cavity where it gives rise to the transversalis abdom- 

 inis muscle. This muscle continues ventralward until within 

 about one centimetre of the mid-ventral line, where it becomes 

 fascia. The other reflected plate of fascia extends subcuta- 

 neously around the body to the mid-ventral line, where it comes 

 in contact with the internal plate, since no muscle takes part 

 in the formation of the body-wall in the mid-ventral region. 

 This tough fascial sheath also envelopes the head, being 

 strongly attached to the median keel in the posterior region, 

 and broadly adhering to the anterior portion of the frontal, the 

 prefrontal, nasal, and premaxillary bones. 



Muscles of the Head. 



Amphiiuna has four dorsal head-muscles : pterygo-maxillaris, 

 masseter, temporal, and cervico-parietalis. The pterygo-maxil- 

 laris arises mainly from the median juncture of the parietalsand 

 the fascia covering the horizontal surface of the frontal. A 

 small portion of the muscle is a continuation of the cervico-parie- 

 talis. Its insertion is on the dorsal side of the pterygoid bone 

 and cartilage. It is clear to be seen that this muscle in Amphi- 

 umds ancestors must have been the anterior part of the cervico- 

 parietalis. The tendons of the temporal, through enlargement 

 and continual activity have usurped almost the entire space of 

 the parietal groove, thereby causing the unused muscle to dwin- 

 dle. The masseter is an exceedingly strong muscle, and arises 

 in two parts. One part originates from the lateral area of the 

 prootic, the other from the anterior curved keel of this bone. 

 The two unite almost at their origin, and extend as a thick, 

 muscular mass to its insertion on the mandible external to the 

 coronoid process. The temporal is the long and strong 

 elevator of the lower jaw. It arises from the neural spines of 

 the fifth, fourth, third, second, and first vertebrae. It is insep- 

 arably joined with its fellow as far as the parietal bone. At a 

 distance forward of this equal to the interorbital space, the 



