MOKPHOLOtiY or CKAXIAL ,M L'SCLES IX SO-MI-: VlilJTEBRATES. 247 



ends o£ the second and third to the third bar, just behind 

 its junction with the processus branchialis. In Rana, at tlie 

 end of uietainorphosis, the cerato-brancliial portions of the 

 branchial bars disappear and the Mtn. niarg'inales also. The 

 upper end of the first levator becomes attached in part to 

 the palato-pterygoid bar and in part to the periotic capsule, 

 the second, third, a.nd fourth to the periotic capsule only 

 (Text-fig. 61). This is also the case in Alytes, Bufo lenti- 

 ginosns, and IVlobates.^ 



According- to Wilder, in Rana clamitans the fourth 

 levator is formed during* metamorphosis by division of the 

 dorso-laryngis into the fourth levator, and dilatator laryngis ; 

 and this is stated to hold g-enerally in Anura. In Rana 

 temporaria, however, the fourth levator is formed in 7 ram. 

 embi:yos, and the dorso-lar^-ngeus not until 7i mm., and the 

 two muscles liave no genetic connection ; and both muscles 

 are present in larva? of Pelobates, Al^'tes, and Bufo lenti- 

 ginosus, of 10, I2h, and 10 mm. respectively, i.e. long before 

 metamorphosis. 



In Rana, late in metamorphosis, the partial origin of the 

 first levator from the palato-pterygoid bar is given up, and, 

 on the atrophy of the cerato-branchials and Mm. marginales, 

 all four levators extend downwards, and their lower ends 

 become attached to the body and processus posterior medius 

 of tlie hyoid bar. 



In 12 mm. larviie of Rana a downgrowth of the lower end 

 of the fourth levator takes place, forming the diaphragmato- 

 branchialis lateralis" (of Schultze). Its upper end becomes 

 attached to the fourth bar, its lower end to the diaphragm. 

 It is innervated by the Xth. It is also formed in Alytes, 



^ Scliultze. in older larvae of Pelol)ates. described all four levatores as 

 arising from the palato-({uadrate l^ar. 



- Schultze gave the name '■ diaphragniato-branchialis medialis " to 

 the nuiscle called " sterno-liyoid " in this paper. He did not desci-ibe 

 the innervation or development of the larval muscles of Pelol;)ates ; his 

 names are purely descriptive, and do not imply that he thought that the 

 two muscles " diaphragmato-branchialis "' and " medialis " have any 

 genetic connection. 



VOL. 56, PART 2. KEW SERIES. 18 



