BY W. J. McKAY. 933 



The muscle is related to the digastic posteriorly, while some 

 fibres of the retractor oris spread over it externally. Internally 

 the muscle hides from view the external pterygoid. 



TJie muscle differs but slightly in all the forms examined. It is 

 supplied by the fifth nerve. Its action is to raise the mandible, or 

 when the latter is fixed to depress the cranium. 



M. PARiETo-MANDiBULARis (muscle of the epipterygoid bone). 



Die vierte Portion of No. 1, Hoffmann, D'Alton. 



On reflecting the masseter and pushing aside the venom gland, 

 a thin rounded muscle is observed lying in front of the anterior 

 temporal muscle. It arises from the prominent projection at the 

 junction of the middle-lateral with the posterior-lateral edge of 

 the parietal bone. It runs downwards and backwards to be inserted 

 on a small area of the upper portion of the middle third of the 

 internal surface of the mandible. The muscle was described by 

 D'Alton, who took it to be a portion of the temporal muscle 

 (tiefste Portion). Hoffmann has likewise described it as portion 

 of the temporal. An important relation is established by a large 

 branch of the third part of the fifth nerve, which emerging from 

 under cover of the anterior temporal muscle winds round this 

 muscle, and separates it from the temporal group. 



In HydrosauTus a similar muscle is present, springing from the 

 parietal, and the superior portion of the epipterygoid (columella) 

 and being inserted on to the mandible. The nerve has the same 

 relation to it as in the snakes. The muscle appears in all the 

 snakes exaaiined, and Sanders (No. 25), has described a muscle 

 similar to this in Platydaclylus and Liolepis. He however says 

 that the muscle is inserted into the pterygoid bone ; this we think 

 is a mistaken observation. He suggests that the muscle corres- 

 ponds to the tensor t^'mpani, but we are at a loss to see on what 

 ground he could found his homology. It may belong to the 

 temporal group, but the relation of the nerve to it forms an 

 obstacle to its being considered so. On the other hand it is supplied 

 by the third division of the fifth nerve. 



