SKELETON AND LARYNX OF.HTMENOCHIEUS BOETTGEKI. 457 



ehirus is represented in the adult Pipa. The other half, how- 

 ever, -will bear a detailed comparisou with the entire hyobranchial 

 skeleton of the adult Pipa. The great alary cartilages (a), so 

 characteristic of the Aglossa, slope outward and backward, and 

 terminate in inwardly directed expansions, which partially 

 overlie the thyrohyals. They extend some distance behind the 

 posterior epiphyses of the thyrohyals in the female, but not 

 in the male {cf. tigs. 1 and 3). The external geniohyoid muscle 

 is inserted about midway between the hyoglossal foramen and 

 the postero-lateral extremity of the alary cartilage (fig. 1, ge), 

 whereas in Xenojpus it is inserted much near^T the foramen, and 

 in Pipa quite close to the postero-lateral border of the cartilage. 

 Lying antero-laterally to the insertion of this muscle is a thin 

 lamellar extension of the cartilage, which finds its exact counter- 

 part in Xenopus.^ bnt not in Pipa. The antero -lateral processes 

 of the basal plate of Xenopus (4. pi. 8, fig. 1, ap) are not repre- 

 sented, unless they are included in the semicircular tract of 

 cartilage which lies in front of the hyoglossal foramen. The alary 

 portion of the hyobranchial skeleton differs somewhat in shape 

 in the two specimens examined, but the paucity of material 

 precludes one from deciding whether these are normal sexual 

 differences. 



In both sexes of Uymenocliirus the thyrohyal bones have the 

 form of tapering rods, as they have in the female Xenopus ; and 

 they are brought into intimate relation with the cricoid cartilage 

 of the larynx, as is characteristic of both Xenopus and Pipa. 

 The posterior ends terminate in large epiphysial cartilages ; the 

 anterior ends converge, and are connected witii one another by a 

 small tract of cartilage, which in the female is continuous with 

 the transverse bar of cartilage running behind the hyoglossal 

 foramen, but which is bound to the latter by a short stout liga- 

 ment in the male. These last relations are exactly those obtaining 

 in the tvfo sexes of Pipa (see 4. pi. 9, fig. 1, i, and fig. 5, i). 



■ The larynx is considerably smaller in the female than in the 

 male, and the thyrohyal bones are shorter, more slender, and set 

 at a wider angle. The floor or ventral wall of the larynx of the 

 female (fig. 3) is largely composed of membrane. It is supported 

 by a horizontal ring of cartilage, from which there project 

 postero-laterally a pair of slender cartilaginous bars. These 

 expand at their extremities into the bronchial cartilages {hr), 

 and are confluent with the posterior epiphyses of the thyrohyals. 



