SKELETON AND LARYNX OP XENOPTJS AND PIPA. 65 



Diseoglossus I find tliat the sexual differences are quite as 

 strongly marked as in Bomhinator, while in JPelobates, Cerato- 

 plirys, and Pelodytes, although the differences are less pro- 

 nounced, they are clearly recognizable. It is highly probable 

 that more extended observations will amplify the list still 

 further. 



In the male Xenopus the larynx, relatively to tlie size of the 

 byobranchial skeleton and to that of the whole body, is con- 

 siderably greater than in the female, but yet, owing to the 

 smaller size of the male as compared with, the female, the actual 

 cubic content of the larynx is about tbe same in both. The 

 larynx of an average male is shorter than that of the average 

 female, but it is broader and more inflated. The roof, alsoy 

 extends proportionately farther forward. The narrow bar of 

 cartilage (PI. 8. figs. 1 and 3, z), which forms the hinder edge of 

 the hyoglossal foramen in the female, is in the male partially 

 replaced by ligament (PI. 8. figs. 4, 5, and 6, V), This is a 

 matter of the highest importance from a morphological point of 

 view, for the substitution has the effect of severing the true 

 basal plate of the byobranchial skeleton from its lateral out- 

 growths in such a way as to make it appear part of the laryngeal 

 skeleton. The basal plate, already so reduced in size, is now 

 separated from all the rest of the byobranchial skeleton, except 

 the thyrohyals. In it Henle (19. p. 17) has described a 

 hexagonal ossified plate, evidently a further development of the 

 small centre of ossification occurring in the same position in the 

 female. I must confess that in the specimens which I have had 

 the opportunity of examining I have found no trace of ossifica- 

 tion in this region. "Whether my specimens were too young, or 

 whether Henle' s specimen was abnormal I cannot say, — the 

 bony plate which he figures is so large in comparison with the 

 remainder of the larynx that it is hardly likely that his observa- 

 tion is at fault. 



The thyrohyals are slightly curved, although straight in the 

 female ; and, owing to the lateral expansion of the laryngeal 

 skeleton proper, they appear to lie more on the ventral side of 

 the larynx than in the female (see PI. 8. figs. 1, 3, 4 and 6). It thus 

 happens that they are not visible in a dorsal view of the skeleton,, 

 whereas in the female very little of the thyrohyal is overlapped 

 by the cricoid cartilage (see PL 8. fig. 3). The floor of the 



lilNN. JOUEN. — ZOOLO&T, VOL. XXYI. 5 



