1893.] TEETEBEAL AND LIMB-SKELETON OF THE AMPHIBIA, 275 



has long ago worked out ^ its fundamental relationships during 

 development to the remaining osseous elements entering into the 

 composition of the adult urostyle. 



vmX. I: 



n c 



\v.alS. 



K«3I 



Pelobaies fiiscus, coccygeal portion of developing vertebral column. 



Fig. 13 in a Tadpole of 92 millim., from beneath. 



Fig. 14 in an older Tadpole of 112 niillim., from the side. 



cc, urostyle ; nc, notochord ; v.a. ix-xi, vertebral arches. 2^ times nat. size. 



In view of this, and of my tadpole proving to be a Pelobatoid, I 

 eagerly availed myself of the beautiful preparations of the larval 

 skeleton of Pelobates fusciis placed upon the market by J"ritsch of 

 Prague. Great was my delight to find that two of the three 

 individuals purchased from him showed the ossification in question. 

 This and certain other genera of living Anura are somewhat 

 remarkable for the detailed mode of development of their vertebral 

 bodies ^ and especially for the late appearance of their centra, those 

 structures not being developed until the arches are in an advanced 

 and directly articulated state. The rod above referred to (cc, 

 fig. 14), which beyond doubt gives rise to at any rate the main 

 portion of that which Goette calls ^ the periosteal component of 

 the urostyle, arises in the interval of time between the formation 

 of the ossific neural arches and their corresponding bony centra. 

 The figures sufficiently show that it first appears beneath the 

 10th pair of arches as ordinarily enumerated {v.a. x), and that it 

 elongates in a backward direction with the superaddition of the 

 11th pair (v.a. xi). There is thus recognizable at this period of 

 growth a provisional inversion of the order of deA^elopment of the 

 .parts — the ossific neural arches appearing before their correspond- 

 ing centra and the ossific body of the urostyle arising prior to the 

 first deposition of the last (] 1th) pair of arches, with which it sub- 

 sequently first unites. In consideration of the conflicting opinions 

 concerning the morphology of the " hypochordal " constituent of 

 the urostyle*, and especially of Goette's refusal to admit this 

 homologous either with entire vertebras or vertebral bodies °, this 



1 Loc. cit pp. 108-111. 



' Cf. Balfour's ' Embryology,' vol. ii. p. 556. 



3 Loc. cit. p. 933, and pi. xi. fig. 196. 



* Cf. Gegenbaur, he. cit. pp. 32-33. 



Loc. cit. p. 393. 



