194 F. H. EDGEWOKTH. 



Muskeln lassen sicli leiclit vom Facialis liervorfolgen."^ 

 He also states that in pig embryos the levator veli palatini 

 and M. uvuhe develop as in man from " Gewebe des 

 Platysma colli das von der vorderen Seite des Oberkiei'er- 

 fortsatzes nach seiner raedialen Seite zielit." 



In 2 mm. embryos of the rabbit the cells which will form 

 the myotome of the mandibular segment cannot be differen- 

 tiated from the other cells occupying the segment. In 

 3 mm. embryos (Text-fig. 76) the myotome is visible, and the 

 walls of the mandibular section of the cephalic coelom are 

 beginning to come together, forming the intermandibularis. 

 The myotome separates from the lateral edge of the inter- 

 mandibularis in 7 mm. embryos. In 13 mm. embryos it has 

 partially separated into external and internal portions, which 

 form the two limbs of a A-shaped mass, the apex of which 

 lies just below the Gasserian ganglion (Text-figs. 94, 95); the 

 external portion is the Anlage of the temporal masseter and 

 external pterygoid muscles; it extends up to the skull in 

 16 mm. embryos, the external pterygoid is cut off" from the 

 internal surface of the lower end of the temporal. The 

 internal portion separates into internal pterygoid and tensor 

 tympani. The intermandibularis forms the mylohyoid of the 

 adult, ; it is covered over, in 10 mm. embryos, by the forward 

 growing interhyoideus. 



The Homologies of the Mandibular Muscles. — Com- 

 parison of the variousways in which the myotoine of the mandi- 

 bular segment develops shows that they may be reduced to two 

 types : (1) That in which the myotome does not divide into 

 upper and lower portions — Ceratodus, Necturus, Triton, Rana, 

 Alytes, Bufo lentiginosus, Pelobates, Lepus. (2) That in 

 which the myotome divides into portions above and below 

 the })alato-quadrate, into levator maxillte superioiis Jind 

 adductor mandibulae — Scyllium, Acipenser, Lepidosteus, Ami;i, 

 Salruo, Sauropsida. 



Driiiier supposed that a portion homologous witli the 



' Beevor and Horsley showed, however, that no movement of the p;ilate 

 is produced in the monkey on iutra-craiiial stimuhitiou of the Vllth. 



