58 WE. W. G. EIDEWOOD OlS" THE HTOBBANCHIAL 



a pair of very large postero-lateral plates, usually described as 

 the " alsB " or "wings" (PI. 8. fig. 1, a) — a most convenieut 

 term, as it merely designates tlie part without expressing its 

 morphological value. The true value of these processes is dis- 

 cussed later, chiefly upon the evidence furnished by a study of 

 the development. The alee are perfectly flat plates of cartilage, 

 with an even margin, slightly pointed posteriorly, and with a 

 blunt notch on the mesial edge at about one-fourth of the length 

 from the posterior extremity. The greatest diameter, at about 

 one-third from the posterior end, is rather more than one-third 

 of the length. Mayer (26. p. 33) says that in the female Xenopus 

 the wings are smaller and thinner than in the male, a statement 

 with which I cannot agree. Bat since he says (p. 29) the male 

 " ist grosser und schlanker gebaut als das "Weibchen," it is evident 

 that his female specimens were not up to the average size, or 

 that his males were exceptionally large. The anterior processes 

 and the alae are of the same thickness of cartilage as the basal 

 plate itself ; but there is a much thinner extension of cartilage, 

 recalling the lamellar expansions of the anterior cornua, which 

 forms the lateral margin. This thins away behind along the 

 external margin of the ala, and is continued forward around the 

 external and anterior edge of the anterior process. It is indicated 

 in Plate 8. fig. 1 by fainter shading. 



The hyoglossal foramen (PI. 8. fig. 1, A), which is such a con- 

 spicuous feature of the hyobranchial apparatus, is mainly closed 

 by membrane : the hyoglossal muscles, which rise up to be dis- 

 tributed to the mucous membrane of the floor of the mouth, pass 

 between the posterior edge of the membrane and the cartilage 

 which bounds the foramen posteriorly (PI. 8. fig. 1, y). The 

 shape of the fontanelle varies ; but it is always oval and elongated 

 in an antero-posterior direction, its greatest diameter lying behind 

 the middle of its length. Henle (19. p. 15), with remarkable 

 introspection, considered that the hinder border of this hole in 

 the basal plate represents the anterior edge of the basal plate 

 of the hyobranchial skeleton of the frog, and that the presence of 

 the foramen is to be explained by the union of the two anterior 

 cornua in front. He based his conclusions almost entirely on 

 the relations of the hyoglossal muscles ; but, as I hope to prove 

 in the sequel, he was fully justified in his determination. Behind 

 the foramen the basal plate is sharply constricted, but it almost 

 immediately widens out behind, and becomes indistinguishably 



