82 ME. W. G. EIDEWOOD OK THE HTOBEAKCHIAL 



front of the basal plate, to be distributed to tbe mucous membrane 

 occupying the position of the lost tongue. It is on the relations 

 of its anterior end that we have to rely for an identification of 

 this muscle as the hyoglossal, for the origin posteriorly is quite 

 exceptional. The hyoglossus in tongued Anura arises from the 

 posterior extremity of the thyrohyal. In Xenopus, therefore, 

 the muscle has undergone considerable diminution in length, 

 arising as it does from the middle of the length of the bone. 

 The hyoglossus internus is not represented in other Anura, and 

 it is all the more curious to note that in the male Xenopus the 

 normal external trunks have disappeared, leaving only this ex- 

 ceptional median portion. 



Betrohyoideus (PI. 10. fig. 1, f). — Arising from the posterior 

 part of the ventral surface of the larynx close to the median 

 line, and running out sideways, is a peculiar muscle which repre- 

 sents the petrohyoideus of more familiar Anura *. It occurs in 

 both sexes of Xenopus, in the female P^jo«, and probably also in 

 the male. Mayer and Henle are silent concerning it : in fact, 

 tliroughout the whole of the literature on IPipa and Xenopus 

 that I have examined, I have met with no reference to such a 

 muscle. The muscle spreads beneath the ventral surface of the 

 larynx in a fan-like manner, breaking up into small bundles of 

 fibres which alternate more or less regularly on the right and left 

 sides. The number of radiating bundles is subject to considerable 

 variation, in some specimens being as small as three, while in one 

 larynx examined as many as seven distinct divisions could be 

 recognized on one side and six on the other. The muscle passes 

 out sideways, ventral to the geniohyoideus internus, and diminishes 

 considerably in width. Then, remaining of the same diameter 

 for the rest of its length, it takes a circuitous course and is 

 ultimately attached to the back of the auditory region of the 

 skull. There is, I think, sufficient evidence here for identifying 

 the muscle with one of the posterior petrohyoids of the frog, 

 most probably the third or fourth of those described by Ecker (13). 

 Geniohyoideus. — The geniohyoideus has already been described 

 by Henle (19. p. 26) as double in Xenopus. The outer division, 

 geniohyoideus externus, arises from the mandible a short distance 

 from the symphysis, and is inserted into the ventral surface of 



* Masto-hyoidien, Duges, 10. p. 125, and PI. vii bis, fig. 44, nos. 20, 21, 22. 

 Styloliyoideus, Walter, 40. P- 36. 

 Petrohyoideus, Ecker, 12, p. 66, and figs. 60, 61, and 205, ^.A. 



