310RPH0L0GY OF CRANIAL MUSCLES IN SOME VERTEBRATES. 215 



and a ventral ceratoliyoideus externus. Examination of 

 sections of 14i mm. embryos shows that there is a stage in 

 which the future digastricus (the " cephalo-dorso-mandi- 

 bularis '^ of Driiuer) forms a levator hyoidei, inserted into the 

 upper end of the hyoid bar^ whilst below the cerato-liyoideus 

 externus the Anlage of the hyomaxillai'is ligament is formed 

 (Text-fig. 55). 



Text-fig. 4-3. 



It is of interest to note that in Siren (Driiner) there is a 

 levator hyoidei, a slip of the cephalo-dorso-mandibularis, 

 i.e. in that animal the primary insertion of the muscle is not 

 wholly lost. 



The interhyoideus^ of Necturus spreads backward behind 

 the hyoid bar in the opercular fold, and this posterior part, 

 at first entirely ventral, spreads upwards laterally external to 

 the cerato-hyoideus externus and depressor mandibulae. There 

 is a similar development of the interhyoideus in Triton, and 



1 Posterior myloliyoid of Mivart and Miss Piatt. 

 VOL. 56, PART 2. NEW SERIES. 16 



