1894.] 



MYOLOGY OF BODENTS. 



255 



seen it at all in the true Hystricomorpha, but it is present in the 

 Dipodidae ; it is also present in all the Sciuroinorpha except Castor. 

 It consists of a round bundle of fibres running across between the 

 two halves of the mandible close to the symphysis ; it is superficial 

 to the mylo-hyoid but deep to the digastric. Its nerve-supply is 

 from the mylo-hyoid of the inferior dental. 



Fig. 1. 



Digastric of Pteromys. 



Mylo-hyoid. — The mylo-hyoid in the Hystricomorpha resembles 

 the same muscle in Man ; in the Sciuroinorpha it is connected 

 posteriorly to the tendinous arch of the digastrics. 



Genio-hyoid. — In the Caviidse and Dasyproctidse this muscle 

 rises by a thin tendon from the symphysis; in the Sciuroinorpha 

 the two muscles tend to coalesce before reaching the hyoid bone. 

 The muscle has the usual human attachments. 



Genio-hyoglossus. — This muscle has the human attachments. In 

 Myopotamus it was noticed that the part running to the tongue 

 was Meshy in its origin, while that going to the hyoid bone was 

 tendinous. 



Styloid Muscles. — The stylo-hyoid rises from the base of the 

 skull just internal to the paroccipital process ; it passes deep to the 

 digastric to be attached to the epihyal cartilage close to the hyoid 

 bone. 



The styloglossus rises lower down than the last from the carti- 



