Dermal Bones of the Skull 



75 



for instance, the prootics are freely visible from above, whilst in 

 P. cultripes a bridge is to be found connecting the secondary dermal 

 bones which overroof the frontoparietal on one band, and the 

 tynipanic, quadratojugal and maxillary on the other. This fronto- 

 parietalo-tympanic bridge encloses, with the prootic, the fenestra 

 posttemporalis (Fig. 2). 



That these formations occurring in Pelohates are notancestral 

 markings, inherited from some Stegocephalous predecessors, as 

 assumed by Boas with respect to the Hemiphractidae^^), seems 

 to be proved by their late ontogenetical appearance. I 

 examined large, nearly metamorphosed larvae of Pelohates (also of 

 P. syriacus Bttg.), where no trace of secondary dermal ossifi- 

 cations could be found; the surface of the frontoparietals and 

 tympanic is in such young individuals (Fig. 3) quite smooth, 

 presenting well defined 

 outlines, and resemb- 

 ling the type obser- 

 vable in Alytes for in- 

 stance; a large fonta- 

 nelle separates the 

 frontoparietals from 

 each other. The men- 

 tioned smoothness of 

 the bones in question 

 proves also that the 

 , , incrustation* ' lat er 

 occurring on them is 

 certainly not a pri- 

 mary structural par- Figure 3. 



ticulartiy. 



On the body the development of the secondary exoskeletal 

 plates is not as limited as on the head, and so the corium might 

 secrete larger osseous plates there, which, simply by means of their 

 anatomical topography, are generally not connected with any endo- 

 skeletal Clements. In some cases, however, (Brachycephalus) the com- 

 ponents of the secondary exoskeleton of the body may also anky- 

 lose to more superficial endoskeletal Clements, in the same way 

 as the primary dermal bones coalesced with the elemen+s of the 

 ancestral endoskeleton, i. e. with the chondroskeleton. The 

 rpof, i. e. the outer surface of these ,,body-plates'* is generally 

 very rugose (cfr. Stegocephalians and Ceratophrys), but this 

 incrustation is not a ,, tertiary** , viz. not a later Stra- 

 tum of lime settled upon the phylogenetically secon- 

 dary exoskeletal plates, but merely represents the 

 structural ,,sculpture" of the respective secondary 



13) Die* Schläfenüberdachung u. d. Palatoquadr. i. ihr. Verhältn. z. 

 nbr. Schädel b. d. Dipnoern u. d. terr. Wirbelt,, Morph. Jahrb., Bd. XLTX, 

 2. Heft, 1914, fide O. Abel, op. cit. p. 316. 



7. Heft 



