SKELETON AND LARYNX OP XENOPIJS AND PIPA. 97 



of the antero-external edge (Plate 11. fig. 1, h) is very constant 

 in its occurrence ; and this also is not unrepresented in the genus 

 Mana. 



The hyoid arch consists of three elements — two large massive 

 lateral cartilages or ceratohyals (fig. 1, ch.), which later will 

 form the anterior cornua of the hyoid apparatus, and a small 

 median cartilage or basihyal (hJi.). There are thus in the hyo- 

 branchial skeleton at this period five distinct and separable 

 cartilages, as has been held to be the case in the tadpole of the 

 common frog from the time of Cuvier (8) onwards. Graupp 

 states (14. p. 433) that inltanafusca tadpoles the whole cartilage 

 is continuous, without fibrous tissue intervening. I have not 

 been able to procure tadpoles of this species ; but I have made a 

 careful examination of tadpoles of suitable age of Rana esculenta 

 and j5. temporaria, and in both of these the five cartilages are 

 very sharply defined. I am inclined to think that the imper- 

 fections of the method adopted by Graupp are largely responsible 

 for his departure from the generally accepted view. As men- 

 tioned above, it is very diflScult to discriminate between embryonic 

 cartilage and fibrous tissue by their histological characters. 



The ceratohyal or lateral hyoid bar is a stout massive cartilage 

 closely wedged in between the branchial cartilage behind and the 

 meckelian cartilage in front. The posterior edge is hollowed out 

 superiorly so as to allow the anterior pointed extremity of the 

 branchial basket to overlap it. The anterior edge of the cerato- 

 hyal is thin, and runs parallel with the attenuated mandible, 

 almost in contact with it. The distance between the outer 

 extremities of the hyoid arch is considerably less than the 

 maximum diameter across the branchial skeleton. The two 

 ceratohyals touch one another in front ; but the posteriorly 

 directed processes of their median ends are separated by the 

 basihyal, and are wedged in between the divaricated ends of 

 the branchial skeleton. The basihyal is cuneiform and pointed 

 anteriorly. Its posterior surface is applied to the branchial 

 cartilage immediately in front of the thyroid bodies *. I regard 

 this m.edian cartilage as the basihyal because of its intimate 

 relation to the ceratohyals ; but I am quite prepared to agree 

 with Parker (34) that when, as in Alytes, six elements instead of 

 five are present in the larval hyobranchial skeleton, the extra 



* I am at a loss to understand why Parker (33. PI. 58. fig. 3, tr.q.) figures 

 the "thyroid glands " close up under the auditory capsule. 



LINN. JOTJRN. — ZOOLOGT, VOL. XXVI. 7 



