Explanation of Plate Y 



Jaw muscles of liana, representing the Anura, and of Cryptobranchus japon- 

 icus, Amphiuma and Amblystoma, representing the Urodela 



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- 

 tromatic group, in front of the squamosal and quadrate, innervated by V 3 , and 

 a posttrematic group behind the squamosal 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 

 (C. m.), 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 tbe adductor mass. The 

 depressor mandibular (D.m.) lies entirely behind the otic region and is inner- 

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

 dibularis of fish (Pollard). 



Fig. 3. — Cryptobranchus japonicus. (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-man- 

 dibularis superficialis (G.m.s.), while the levator maxillae superioris may be 

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

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

 .•interior is large. 



Fig. 4. — The same seen from above. 



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



Figs. 6 and 7. — Amblystoma. (Muscles mainly after Driiner.) 



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

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



