"A- 



878 Dr. A. Giintber on Sexual Differences 



tremities of the t)niipanic bones (24^'''), longest in its median dia- 

 meter (18'"), and highest in a vertical from a prominent crest of 

 the OS petrosum (9|'"). The latter extraordinary elevation of the 

 posterior part of the skull is not only effected by the crest above 

 mentioned, but chiefly by a most powerful development of the 

 tympanic bone. Thus the upper surface of the skull, instead 

 of being flat, as in other frogs, descends steeply to the margins 

 of the jaws. In viewing the skull from behind, we find that the 

 occipital vertebra itself is as much depressed and low as in other 

 frogs, leaving beneath a wide free space for the pharynx, spacious 

 enough to admit the passage of the largest prey which these 

 gigantic frogs are capable of holding. The sutures between the 

 exoccipital and the neighbouring bones have entirely disappeared. 

 There is, immediately below and at the exterior of each of the 

 condyli, a very distinct opening for the passage of nn. vagus and 

 glossopharyngeus ; above and externally, a thick and obtuse pro- 

 cess — probably the place of junction of the exoccipital and os 

 petrosum, and homologous with the crista occipitalis of the Car- 

 nivora; it affords a broad base for the insertion of the muse, 

 temporalis on the anterior side, and for that of a part of the 

 muscles of the neck on the posterior. This process is relatively 

 larger in Cystignathus. The ossified dermal plate*, which covers 

 the parietal region, projects with a sharp edge, somewhat above 

 the process mentioned, forming a small recess below. The os 

 petrosum is stronger than in any other Batrachian. We may 

 distinguish in it three portions — one joining the occipital, and 

 two for the suspension of the tympanic. The former, or internal 

 portion, passes at the base of the skull, without visible interrup- 

 tion or suture, into that of the other side and into the basiocci- 

 pital ; it is anteriorly excavated, with a large round foramen for 

 the n. trigeminus f and has a low crest at the pharyngeal side. 

 The two outer portions, a superior and an inferior, which in other 

 frogs form a more or less deep fork, are here united by a thin 

 bony plate with a very small opening, which is closed in the 

 living animal by a cartilage. The superior portion widens very 

 much above, and is covered with a broad bony dermal plate, 

 which projects posteriorly in a very prominent crest t, and ex- 

 tends anteriorly over the mastoid process; at its inner side it emits 

 a bony bridge reaching to the frontal bones and separating, from 



* The dermal plates form, in fact, one continuous covering of the upper 

 surface of the skull; but the description will be clearer by describing 

 separately certain portions of it corresponding to the bones hidden be- 

 neath. 



t This crest is entirely absent in other Batrachians, but well developed 

 in the order of the Chelonii, in which, however, it has a longitudinal direc* 

 tion, whilst here it is transversal. 



