Ex PI. A. NATION OF Pl.ATE X 



Jaw muscles of typical mammals : Didelphys, Solenodon, Miis, ami Homo 



In mammals the jaw musck-s in front of the auditory meatus are derived 

 from the capili-mandibularis of reptiles and are Innervated by the nerve V3. The 

 depressor mandibulje of the reptiles has disappeared and is functionally re- 

 placed by the digastric which is originally a compound muscle characteristic 

 of marsupials and placentals. The posterior belly of the digastric {Dig. p.) 

 Iti'cbably represents a separate slip of the stylohyoideus, both muscles being 

 innervated by closely associated branches of the seventh nerve. The anterior 

 belly (Dig. a.) belongs with the ventral throat muscles and is innervated by 

 the mylohyoid branch of \ ,. 



h'm. 1. — Didelphi/s. ISupei-ficiai muscles. 



In correlation with the carnivorous habits and orthal jaw motion the tem 

 poralis and masseter are both powerfully developed, while the external ptery- 

 goid (Fig. 2) is relatively small. The anterior and posterior bellies of the 

 digastric (Diff. a., Dig. p.) are in the normal mammalian position. 



Fig. o. — Solenodon. Superficial muscles. 



The masseter is considerably enlarged and its principal attachment is not on 

 the slender zygomatic arch, but on the masseteric tubercle of the maxillary 

 beneath the orbit. This is often the case in animals with piercing front teeth. 

 The jaw muscles as a whole are of the carnivorous type. 



Fifi. 4. — Solenodon. 



Deep muscles, showing the weak external pterygoid (Pt. cxt.). 



Fig. 5. — Mus. Superficial muscles. 



The masseter is extended forward beneath the zygomatic arch in front of 

 ilie orbit, crossing the temporalis n(>arly at a right angle. 



l-'iG. G. — Mus. Deep muscles. 



Fig. 7. — Homo. Superficial muscles. 



Fig. 8. — Homo. Deep muscles. 



