154 ANNALS NEW YORK ACADEMY OF SCIENCES 



reptilian jaw gave up its primary function and was taken over into the 

 service of the anditory organs. It retains its old relations with its inser- 

 tion on the handle of the malleus (in reptiles it was inserted on the retro- 

 articular process of the mandible and on the prearticular). The levator 

 veli palatini seems to represent a part of the same pterygoideus anterior 

 that has changed its relation slightly to serve in the region of the mam- 

 malian palate. 



(9) The region innervated by the facialis has changed somewhat in 

 the mammals. The depressor mandibular of the reptiles has given rise 

 to the m. stapedius of the mammals and the rest of the muscle has dis- 

 appeared. 



(10) The posterior belly of the digastric of mammals appears to be a 

 new development that has come from the remnants of the posterior part 

 of the second constrictor (C 2 sd) of reptiles. It is thus believed to be a 

 new muscle which has nothing to do with the "Digastric" of the reptiles, 

 although it has the same functions and the same innervation. To this 

 posterior belly has been added or grafted on at the anterior end one of 

 the long ventral Y 3 muscles to make the anterior belly of the mammalian 

 digrastic. 



(11) The slip that functions as the m. stapedius in mammals appears 

 to have started in the reptiles and has been retained from the depressor 

 mandibular. This muscle, which is connected with the distal end of the 

 stapes in mammals, started in the reptiles and reached its perfected con- 

 dition when it was drawn into the middle ear in the course of the trans- 

 formation of the mammal-like reptiles into the true mammals. As men- 

 tioned above in the sections on birds and reptiles, the future stapedial 

 muscle was in the right position in the reptiles, where the depressor 

 touches the distal end of the stapes, so it is not difficult to imagine how 

 the depressor gave off a slip that became the future stapedius muscle. 



Kelations of the Jaw-Muscles to the Temporal Fenestra 



of Eeptiles 



The following from Gregory and Adams (1915) summarizes their 

 observations on the relations of the jaw-muscles to the temporal fenestra : 



(1) That in primitive vertebrates the chief temporal muscle-mass 

 (adductor mandibular of sharks) was originally covered by the dermal, 

 temporal skull-roof. 



(2) That in modernized Amphibia and Keptilia, as well as in Aves 

 and Mammalia, one or more slips of the primitive adductor mass had 

 secured additional room for expansion by perforating the temporal roof 





