Explanation of Plate Y 



Jaw muscles of Raiia. representing the Aiiura, and of CruptobranchiiH japoii- 

 icus, Amphiuma and Anihlystoma, representing the Urodehi 



In all modern Amphibia, owing to the loss of most of the derm bones cover- 

 ing the occiput and temporal region, the jaw muscles lie immediately beneath 

 the skin and extend above the parietals. The muscles are divided into a pre- 

 trematic group, In front of the squamosal and quadrate, innervated by V^, and 

 a posttrematie group behind the sciuamosal and quadrate, innervated by VII. 



Figs. 1 and 2. — Rana. (Muscles after Ecker and Wiedersheim.) 



The superficial muscles after the removal of the maxilla are shown in Fig. 1, 

 and the deep muscles in Fig. 2. 



The adductor mass of fishes is now represented by the capiti-mandibularis 

 {Cm.), which is divided into anterior and posterior slips running respectively 

 from the squamosal and quadrate to the mandible. The deep part runs from 

 the under side of the squamosal to the mandible. The pterygoideus anterior 

 ( Pt. ant. ) probably represents the deepest part of the adductor mass. The 

 (l(>pressor mandibulse (D.m.) lies entirely behind the otic region and is inner- 

 \ ated by the 7th nerve ; it may have been derived from the retractor hyoman- 

 dibularis of fish (Pollard). 



Fig. 3. — Cryptohranchus japonUms. (Muscles mainly after Humphrey.) 



The deep anterior part of the adductor mass of fish is here represented by 

 the much-enlarged pterygoideus anterior, the outer part by the capiti-mau- 

 <libularis superficialis {C.m.s.), while the levator maxillse superioris may be 

 represented by the capiti-mandibularis profundus {Cm. p.) and pterygoideus 

 posterior. The depressor mandibulte is divided into two parts, of which the 

 anterior is large. 



Fig. 4. — The same seen from above. 



Fig. 5. — Amphiuma. (Muscles mainly after Driiner.) 



Figs. 6 and 7. — Amhli/.*<t(')n)(i. (Muscles mainly after Druner.) 



The superficial and middle layers of the jaw muscles are seen in Fig. 6, and 

 I lie deep muscles after the reflection of the capiti-mandibularis in Fig. 7. 



