DO ME. "W. G. EIDEWOOD ON THE HYOBEA]S"CHIAL 



more circular in Pipa than in Xenopus, but tends to become- 

 elliptical with increasing age. Even in very old specimens the 

 antero-posterior diameter is not vastly in excess of the trans- 

 verse, so that the hole is never so drawn out as in the middle- 

 aged Xenopus. As in this latter genus, the anterior three-fourths 

 of the foramen are closed by a fatty membranous tissue. 



The antero-lateral processes oi Xenojms (PI. 8. fig. 1, ap.) are 

 missing, and the wings are of an entirely different shape. The- 

 stalk of attachment to the axial parts of the hyobranchial 

 skeleton is very narrow. The basal plate is much constricted a 

 short distance behind the hyoglossal foramen so as to be divided 

 into two parts connected by an isthmus (PL 9. fig. 1, i). The 

 anterior portion forms the hinder border of the foramen, the 

 posterior enters into the constitution of the floor of the larynx, 

 It is from the posterior edge of the latter portion that ,the 

 thyrohyals arise. Henle states (19. p. 16) that the isthmus 

 is ligamentous as it is in the male ; but Gronberg (18. p. 635) 

 has already corrected this error. The hyobranchial skeleton o£ 

 the old female differs in numerous particulars from that of the 

 female just sexually mature. The foramen, as already pointed 

 out, is elliptical instead of circular, the pointed cartilage in front 

 is longer and thinner, the wings are more incised on their inner 

 margin, while the stalks are narrower and more elongated. 

 Breyer states (4. p. 14) that the "lamina" or wing of the hyo- 

 branchial skeleton of Pipta is longer and narrower in the male 

 than in the female. Meckel (28. Theil iv. p. 3.38) agrees with 

 Breyer that the wing of the female Pipa is broader than that of 

 the male, but says it is longer also. Mayer (26. p. 32) affirms 

 that the wing is especially broad and strong in the male. The^ 

 difference in proportion is, however, in my opinion, one of age, 

 not of sex. 



Laetngeal Skeletoi^ of Pipta americana. 

 The first mention of the larynx of Pipa was made in 1764, by 

 Fermin, who describes it in the male as the lambdoid bone *; 



* Fermin, 13- p. 150. " * * * deux cavites distinctes et separees I'une de 

 I'autre par un diaphragme, attache a un Os triangulaire, qui a la forme d'un 

 Q grec, que I'on pourroit appeler I'os Lamhdoide. II est situe au dedans de la 

 cavite generale, ou sa base se trouve fixee par un fort ligament a la partie 

 superieure du Sternum ; et duquel il deborde un pen. De la base du meme Os 

 sortent deux ligamens assez forts qui s'implantent dans la partie mojenne de 

 la machoire inferieure." 



