SKELETON AND LABYNX OF XENOPUS AND PIPA. 57 



simplest of the four, we experience less diflBculty in instituting a 

 comparison with the more familiar toDgued Anura; and, after 

 having definitely settled the morphological value of each skeletal 

 part, we can readily proceed to ascertain how the more modified 

 parts in the other three are related to those of the first. As in 

 other Anura, so in the Aglossa, it is impossible to draw, in the 

 hyoid apparatus of the adult, a sharp line of demarcation between 

 those structures which are hyoidean and those which are branchial 

 in origin. The anterior cornua representing the main portion 

 of the hyoid arch are present in Xenopus, but disappear during 

 metamorphosis in Pipa (see p. 108). In both genera, however, 

 there is a relic of hyoidean cartilage in the median cartilage 

 situated in front of the hyoglossal foramen. 



The first figure published of the hyobranchial skeleton of 

 Xenopus is that of Mayer (26. Taf. 3. fig. 7). This is fairly 

 correct in detail, but fails to show the hyoglossal foramen. 

 Henle's figure (19. Taf. 2. fig. 1), also of the female sex, is far 

 superior. The figure which Parker gives (33. PI. 58. fig. 5) is, 

 on the whole, less useful than Henle's. It shows that the larynx 

 -lies between the thyrohyals, but it furnishes no details of the 

 relationship. A similar figure open to the same objection is 

 given by Grronberg (18. p. 636, fig. A, ii.), and two others, with 

 the said details introduced though incorrectly, by Wilder (42. 

 PL 21. figs. 58 and 59). 



In the female Xenopus the anterior or hyoidean cornu (PI. 8. 

 fig. 1, ch.) is broad and flat, and consists of a rod-like axis, ex- 

 panded on its inner and outer edges into very thin and delicate 

 plates of cartilage which have hitherto escaped notice. At the 

 upper posterior end of the arch the axis is unaccompanied by its 

 lamellar expansions ; it takes a sharp curve upwards and out- 

 wards, and is attached by ligament to the skull about 3 mm. 

 from the articular head of the quadrate. At their anterior or 

 median extremities the cartilaginous rods of the right and left 

 cornua unite at a very obtuse angle. The external lamellae are 

 continuous in front of this union ; but the internal or posterior 

 expansions stop at some distance from the median line. Prom 

 the point of union of the cornua there extends back a median 

 rod of cartilage (PI. 8. fig. 1, ch.'), very slightly, if at all, broader 

 than the axes of the cornua. The basal plate or body of the 

 hyoid is produced outwards into two smaller anterior processes 

 (PI. 8. fig. 1, ap.) fitting closely behind the anterior cornua, and 



