SKELETON" AND LARYNX OF XENOPUS AND PIPA. 91 



It now only requires an extension o£ the tendons to meet below 

 the glottis to complete the resemblance. The changes in the 

 relative positions of" the bellies of the muscles would follow as a 

 consequence of the rotation of the glottis. The dilator anterior 

 would straighten out and occupy a dorsal position, leaving the 

 greater dilator on the ventral surface of the larynx and its acces- 

 sory slip laterally. As an alternative view, it may be suggested 

 that the ventral muscle, S 3, which Grronberg says is absent in 

 the frog, is the equivalent of that curious muscle which in Disco- 

 glossus and Alytes runs from the ventral surface of the posterior 

 epiphysis of the thyrohyal to the ventro-anterior point of the 

 arytenoid cartilage. Wilder figures the muscle in Alytes (43, 

 Taf. 20. figs. 36 and 37) and regards it as the displaced constrictor 

 laryngis, which otherwise must be admitted to be absent. 

 "Whether Wilder's interpretation is correct must remain for 

 future investigation to decide : the two muscles do not unite in 

 front of the glottis as do the constrictors of the frog. 



These conclusions savour, no doubt, of conjecture, being based 

 on the study of figures only, drawn by two different authors, each 

 of whom has examined the muscular system of one sex only. In 

 spite of the interesting union of the tendons ^2 antero-ventrally 

 to the glottis, I am not disposed towards an unqualified accept- 

 ance of Grronberg' s determination of the muscles as the con- 

 strictors of the common frog. An exhaustive study of the 

 muscles, extrinsic as well as intrinsic, of the larynx of the male 

 and female Pipa would most assuredly repay any investigator 

 fortunate enough to have the necessary material at his command. 



Development op the Htobranchial and Laryngeal 



Skeleton. 



The development of the hyobranchial and laryngeal skeleton 

 of the Aglossa is practically unknown. Parker's treatise on the 

 development of the skull of Xenopus and Fipa (33) is the only 

 work to which we can turn for information ; and this does not 

 furnish much. On comparing the hyobranchial skeleton of the 

 tadpoles of Rana, Alytes, Felohates, and Biifo, one is struck by 

 the uniformity of structure that exists in the difterent genera 

 during the earlier stages of development ; and the observations 

 now to be recorded show that the skeleton of Xenopus and Pipa 

 conforms to the general ground-plan. The various modifications 



