410 DAVIDSON BLACK 



In anurans (Rana) only two muscles are innervated by the 

 VII nerve : the m. depressor mandibulae and the m. subhyoideus. 

 The former muscle acts as its name implies, as a depressor of 

 the lower jaw and also, by traction on the tympanic ring, as a 

 tensor of the tympanum. The m. subhyoideus arises from the 

 posterior portion of the cornu principale of the hyoid close to the 

 skull, and extends ventro-mediad just caudal to the m. sub- 

 maxillaris to be inserted into a tendinous raphe common to it 

 and the latter muscle. It acts as a weak levator of the caudal 

 part of the buccal floor and in common with the m. submaxil- 

 laris, assists in deglutition and inspiration. Neither of these 

 muscles under normal curcumstances plays an important part 

 in respiration, and the action of both may be dispensed with 

 without seriously interfering with the respiratory mechanism.* 

 It becomes evident that in anurans the facial and trigeixiinal 

 musclature together form a complex which is primarily con- 

 cerned in effecting movements of the lower jaw and plays but 

 a relatively unimportant accessory role in purely respiratory 

 movements in these forms. 



In urodeles the facial musculature is more extensively rep- 

 resented and more primitively arranged than in anurans. In 

 Siren lacertina an unusual and primitive condition obtains in 

 the arrangement of the m. depressor mandibulae (m. cephalo- 

 dorso-mandibularis) so that some of the fibers of this muscle 

 retain their insertion on" the hyoid arch and constitute the m. 

 levator hyoidei. The facial nerve is distributed also to the 

 following muscles in Siren: mm. interhyoideus, interbranchialis 

 and cerato-hyoideus externus (v. Norris, 46; Driiner, 19). In 

 Cryptobranchus (McGregor, 42; Driiner, I.e.) the facial mus- 

 culature is represented as follows: mm. depressor maxillae in- 

 ferioris, mylohyoideus posterior and sphincter colli (cephalo- 

 dorso-pectoralis). In Triton (Coghill, 17; Driiner, I.e.) the 



* Langendorff (41) has observed that rhythmical respiratory movements con- 

 tinue in R. esculenta after the isolation of a segment of the medulla about 5 mm. 

 in length between the exit level of nerve VII and that of the caudal X rootlet. 

 Reference to fig. 9 B makes it evident that within such a segment only the motor 

 IX-X nuclei of the efferent centers will be retained intact. 



