188 F. H. EDGE WORTH. 



Meckel's cartilage (the process of separation into anterior and 

 posterior portion beginning- in 9^ mm. embryos and being 

 completed in 14 mm. embryos). 



In Ceratodus the myotome of the mandibnlar segment 

 spreads upwards lateral to the Gasserion ganglion (Text-fig. 

 39), and separates from the lateral half of the intermandibularis 

 between stages 40 and 42 (of Semon). It divides into outer 

 and inner portions — pterygoid^ and temporal" — the former of 

 which, in stage 48 (Text-fig. 46), arises from the trabecular 

 wall, and the latter from the anterior and outer surface of the 

 quadrate. The intermandibularis^ joins its fellow in a median 

 raphe and becomes attached laterally to Meckel's cartilage ; 

 its posterior edge extending backwards underlies the fore 

 part of the interhyoideus (Text-figs. 41, 45). 



In Necturus (Miss Piatt) the mesothelium of the mandi- 

 bular arch (here interpreted as "myotome") divides into an 

 internal part, the temporal (here called, following Driiner, the 

 "ptei-ygoid"), and an external part, the masseter. In Triton 

 the myotome of the mandibular segment also divides into an 

 internal and an external part; the upper end of the internal, 

 pterygoid, part extends up to the side of the skull; the 

 external part, at first arising from the suspensorium only, 

 divides into an outer portion, the masseter, which keeps this 

 origin, and an inner portion, the temporal, which extends up 

 to the auditory capsule. 



The intermandibularis of Necturus^ remains single, its 

 posterior edge underlies the anterior interhyoideus (Text-fig. 

 55); in Triton the intermandibularis (in larvae between the 

 lengths of 8^ and 10 mm.) divides into anterior and posterior 

 parts,^ the latter of which partially underlies the inter- 

 hyoideus. 



' Pterygoid of Jaqiiet. 



" Adductor mandiljiilae seu digastricus of Jaqiiet. 

 •' CoUiv of Rnge ; uiylohyoidens pars anterior of Jaquet. 

 ■* Mylohyoideus anterior of Mivart and Miss Piatt. 

 •^ Interniaxillaris anterior and posterior of Wiederslieim ; inter- 

 mandibularis anterior and posterior of Driiner. 



