:\[OEPHOLOaY OF CRANIAL MUSCLES IN SOME VERTEBRATES. 253 



stenio-mastoid of the adult. The portions of the branchial 

 myotomes below the Anlageii of the trapezius have dis- 

 appeared in 7 mm. embryos. 



In the pig- the lower end of the first branchial myotome 

 persists (Text-fig. 98), and forms the intei'arcualis ventralis I 

 s. branchio-hyoideus (Text-fig. 99). This uuiscle is also con- 

 stantly present in the dog/ and in Mouotremes,"- and is occa- 

 sionally present in man.' In Monotremes there is also an 

 interarcualis ventralis III passing from the third to the 

 second branchial arch.*^ 



On thk Homologies between the Bkaxchial Muscles of 

 VARIOUS Vertebrates. 



(1) The Hypobranchial Cranial Muscles. — The 

 lower ends of the branchial myotomes develop into longi- 

 tudinal muscles — interarcuales ventrales, and coraco bran- 

 chiales — in Selachii, Teleostomi, Dipnoi, Amphibia, and 

 Mammalia. Their innervation varies. Those which remain 

 in their segment of origin, or nearly so, extending forward 

 to the ventral end of the next anterior branchial bar or 

 hyoid bar (or additionally and subsequently to the next pos- 

 terior bar, in Amia, and probably Polypterus senegalus) 

 are innervated by the corresponding branchial nerve, IXth or 

 branch of Xth, or by this and the next anterior branch. 

 This holds for the interarcuales ventralcs of Amia, 

 Polypterus senegalus, Sahno, Ceratodus, Amphibia, and 

 Mammalia. The interarcualis ventralis I of Sauropsida 

 (branchio-hyoideus or branchio-mandibularis) is an exception 

 to the rule; it is innervated by the Xllth. 



A coraco-branchialis, or pharyngo-clavicularis externus and 

 internus, developed by back ward growth from the last branchial 

 myotome, i.e. fourth in Polypterus senegalus, fifth 



' Kerato-hyoideus of EUenberger and Baum. 



* Interhyoideus of Duhois. 



•'' Kerato-tliyro-hyoideus of Sliattuck. 



■* Interthyroideus of Dubois. 



