1897.] SKELETON OF PBLODITBS PUNO'XATIJS. 589 



Stage 6. Distance from snout to root of tail, 19 mm. Length of 

 tail, 2'5 mm. Length of hind limh, extended, 27 min. Length of 

 fore limb, extended, 11 mm. (Plate XXXV. fig. 6.) ^ 



At this stage the branchial arches are on the verge of dissolution, 

 and it requires the very greatest care in dissection to avoid losing 

 the relations o£ the dismembered parts. The whole aspect of the 

 hyobranchial skeleton has changed. In the middle is a faint 

 Y-shaped mark representing the lines of junction of the two hypo- 

 branchial plates and the basihyal. The mesial edges of the 

 ceratohyals can still be identified, but they are wider apart than 

 before. The hyoglossal notch is reduced in size by the addition of 

 cartilage ( p«., fig. 6) to the front half of the antero-internal free 

 edges of the ceratohyals. Although this new cartilage is confluent 

 with that of the ceratohyal, what was previously the edge of the 

 latter is still well-marked, thus showing that the new process is 

 not due to an outgrowth of the original hyoidean cartilage. These 

 new cartilages represent the anterior processes of the hyoid 

 apparatus of the Frog (^^a., fig. 11) which develop late and about 

 this stage. In fact, the figure which Gaupp gives of the hyoid of 

 the metamorphosing tadpole of Hana fusca with tail reduced to 

 5 mm. (5. Taf. 19. fig, 8) agrees tolerably well with fig. 6 o£ 

 Pelodytes. Graupp applies the name " processus anterior" indiffer- 

 ently to the most anterior point of the original ceratohyal 

 (" hyale ") and to the later developed cartilage which constitutes 

 the foremost part of the adult hyobranchial skeleton ; but, seeing 

 that the latter has a morphological significance different from the 

 former, and is, moreover, absent in such genera as Alytes, Disco- 

 glossus, and Bombinator possessing the former, I have elected to 

 restrict the application of the term to the latter. Parker's 

 terminology does not help matters, but rather tends to confusion, 

 for he marks these anterior processes of the adult hyoid as parts 

 of the ceratohyals (13. pi. 13. fig. 10), as hypohyals (pi. 5. fig. 4), 

 as epihyals (pi. 15. fig. 14), and as extrahyals (pi. 43. fig. 6), 

 without offering any explanation of the want of uniformity. 



The backward slope of the ceratohyals is now very strongly 

 marked and the posterior parts are becoming reduced in width. 

 The terminal articular surface is quite small compared with its 

 previous extent, and the articulation will shortly give place to a 

 rigid connection with the auditory cartilage. The thyrohyals 

 continue to grow, but their posterior extremities are stiU capped 

 with unabsorbed ceratobranchial cartilage. The outlines of the 

 branchial arches are very indistinct, the softness of the cartilage 

 making it difiicult to distinguish them from the surrounding 

 connective tissue and pharyngeal mucous membrane. The tri- 

 radiate cartilage at the proximal end of the second and third 

 branchial arches appears to be constant in its occurrence, and is 



1 These measurements are those of the figured specimen, which is slightly 

 smaller than the average; but if the above figures be multiplied by \l- the 

 measurements will be seeu to be intermediate between those of tht; specimens 

 representing Stages 5 and 7. 



Pboc. Zool. Soc— 1897, No. XXXIX. 39 



