HYOBRANCHIAL APPARATUS OF SPELERPES 531 



plate with thickened lateral edges. It is notched at its apex, and 

 fits around the middle of the shaft of the first basibranchial to 

 form a more or less freely movable articulation. Posteriorly, as 

 shown in cross-section (figs. 9 and 10), it seems to hold the basi- 

 branchial and proximal ends of the second epibranchials within 

 its concavity, as in a trough. Its lateral thickenings are pro- 

 longed into short, stout shafts which undoubtedly represent the 

 distal ends of the first ceratobranchials and with which the long, 

 heavy first epibranchials are articulated. In addition to the 

 lateral projections is a median, posterior one (probably the 

 second basibranchial, ^ ending in the widening of the cartilage 

 which, in adult life, becomes ossified to form the os thyreoideum. 

 Thus, it is evident that the plate is, in reality, a fusion of three 

 cartilages, the first ceratobranchials and the second basibranchial., 

 This makes it difficult to determine just what elements are 

 actually involved in the first branchial arch. 



The second branchial arch, however, quite plainly consists of 

 a pair of cerato- and a pair of epibranchials. The second cerato- 

 branchial is a short, slender cartilage which articulates, proxi- 

 mally, with the posterior end of the first basibranchial and, 

 distally, with the proximal end of the long, delicate second 

 epibranchial. 



The third branchial arch is represented by a delicate epi- 

 branchial alone, which articulates proximally with the median 

 edge of the second epibranchial; the fourth arch, merely by a 

 raphe in the muscles as in Necturus, and the fifth, represented 

 in the lunged forms by the arytaenoids, has disappeared entirely. 



The branchial plate is the most significant feature of the visceral 

 skeleton of the larva. Although it is apparently a universal 

 phenomenon among larval Salamandrids'^ and is unmistakably 



- In calling this cartilage the second basibranchial I follow Wiedersheim, 

 whose nomenclature of the hyobranchial skeleton I have used throughout this 

 paper. As it is not absolutely proved that this is morphologically the second 

 basibranchial, many zoologists, noticeably followers of Gegenbaur, prefer to be 

 non-committal and call it 'copula.' 



^ In retaining the term 'Salamandrid' as a convenient method of designating 

 the Urodeles that undergo complete metamorphosis, I am aware that recent 

 systematists no longer make this distinction. 



