in the Bones of some Frogs and Fishes. 38S 



selves, but also by bony plates, of decidedly dermal nature, and 

 so joined to the primary bones that they appear to be parts of 

 them. The most interesting part of this dermal structure is that 

 which, coming from the mastoid process, separates the fossse 

 temporalis and zygomatica from the orbit. But this separation 

 is merely external ; internally these cavities form one only, as 

 in the other Anura. 



If we look for a similar structure of the bones surrounding 

 the eye in other cold-blooded Vertebrata, we must compare it 

 with the temporal bridge of the Chelonii and many Saurii, and 

 the infraorbital ai'ch of most of the Teleostei and Ganoidei — the 

 former being formed by primary bones of the skull, the latter 

 being considered as part of the dermo-skeleton. In Ceratophrys, 

 Cultripes, and Cahjptocephalus, we have elements homologous with 

 both. Having skulls of adult animals only, I am not enabled 

 to show the boundary-line between the endo- and exo-skeleton 

 in all the parts; but an examination of the young will un- 

 doubtedly show that the base of this bony ring round the orbit 

 is formed by bones homologous with the posterior frontal, oa 

 zygomaticum, and processus mastoideus, as in Chelonii and 

 Saurii^, and that it is completed and covered by dermal plates 

 situated between the frontal and maxillary bone, — homologous 

 with the infraorbital arch of Fishes. Even the external simi- 

 larity of the skull of the Batrachians mentioned, to that of 

 the Chelonii, is very great : the temporal bridge is relatively 

 narrow in Ceratophrys, leaving posteriorly a distinct round 

 open space (the fossa temporalis), with a free entrance from 

 the upper surface of the skull ; it is exactly the same in the 

 skull of Testudo, Emys, &c. In Cultripes provincialis the bridge 

 is very broadf, covering the fossa temporalis above, and leaving 

 an entrance from the back part of the skull only : it is exactly 

 similar in the skull of Chelonia %, where the os frontale posteriua 

 extends behind further than in any other Tortoise. In Calyp^ 



* The arrangement of the bones forming the temporal arch varies a 

 little. In many Chelonii and most of the Saurii it is formed by the os 

 frontale postering, zygomaticum, and quadrato-jugale (Stann. und Siebold, 

 Zoot. Vert. p. 159). In a skull of Emys Dhongoka, I find the bones very 

 well separated from one another by sutures. The bridge is here formed 

 by the os frontale posterius, a zygomatic bone divided into two parts, and 

 by a part of the os quadrato-jugale, likewise separated from the posterior 

 part by a suture. These sutures are not very distinctly marked in the 

 figure given in Dr. Gray's Cat. Shield Reptiles, t. 36. f. 1. 



t Cf. Uuges, Recherch. Batrac. p. 15, pi. 2. f. 11, 13. In a specimen in 

 the British Museum, the temporal arch is not quite so large as it is figured 

 by Duges, yet fully covering the groove beneath. This, however, may 

 depend on age. 



:|: This similarity has been observed also by Bibron (cf. Dum. & Bib, 

 yiii. p. 448) ; but he refers it to Calyptocephalus. 



