SKELETON AKD LAKTNX OF XENOPUS AND PIPA. 109 



unosaified and still readily separable from tlie larynx proper. The 

 tliyrohyals have increased in length so that their extremities can 

 be seen projecting beyond the sides of the larynx. Their ex- 

 tremities have also become dilated. The al^e have enlarged very 

 considerably, and the maximum transverse diameter of the hyo- 

 branchial skeleton is now three times the width of the larynx. The 

 backward growth of the alse is even more remarkable than their 

 increase in width. The line joining the extremities of the thyro- 

 hyals passed behind the alae in Stage Y., with a considerable 

 distance to spare. In the present case it passes approximately 

 through the centres of the now oval alary plates. 



The hyoglossal foramen is nearly circular in shape and is much 

 smaller than before. The cartilage bounding the foramen has 

 been greatly reduced in thickness, and the anterior tapering 

 process (PI. 11. fig. 9, cli'.) is now as sharply pointed as in the 

 adult. The larynx is still remarkably different from that of the 

 adult. This is a noteworthy fact, because Wilder (42. p. 306) 

 states that in Bana tadpoles, the caudal stump of which has not 

 yet disappeared, the larynx is practically in the adult condition, 

 No peculiarities which might be attributed to sexual differences 

 were to be seen iu the larynx of any of the specimens examined. 

 Since, however, the reproductive organs were not sufficiently 

 advanced to enable me to determine the sex, it was not to be 

 expected that any of the secondary sexual characters sbould be 

 recognizable. 



The arytenoid cartilages have the form which obtains in most 

 adult Anura ; they are pointed in front and are closely applied 

 to one another by their thin dorsal borders. Their broad pos- 

 terior ends fit closely into the ring of the cricoid cartilage, the 

 ventral portion of which is produced forwards to furnish 

 additional support (see figs. 11 and 12). The dorsal portion of 

 the cricoid ring has the form of a band running transversely, and 

 both anterior and posterior edges are nearly straight. The sides 

 are more extensive than in Xenopus Stage III. (see fig. 10), and 

 the floor, which, is roughly triangular in shape, is deeply incised 

 behind. A comparison between this embryonic larynx and the 

 adult larynx of Bomhinator (fig. 13) is very instructive. The 

 bronchial processes (hr.) of the latter are not represented, and 

 the roof of the cricoid is not so expanded, but otherwise the 

 resemblance is very close. The ventral position of the thyro- 

 hyals with regard to the larynx in Pi^a is of course exceptional. 



