iSi Dr. A. Giinther on Sexual Differences 



more likely to have given rise to this opinion than some of 

 the large species of Cystignathus, In the first place, it is by the 

 exceedingly wide cleft and the enormous cavity of the mouth 

 that the Horn-frog is enabled to seize such large animals. We 

 will compare in this respect the skull of a female Cystignathus 

 lahjrinthicuSf which in the size of the body rather exceeded that 

 of the female Horn-frog, the skull of which I have described : — 



Horn-frog. Cyst. lab. 



Greatest width of the cavity of the mouth 31 lines 23 lines. 



„ length of ditto 25 „ 20 „ 



„ depth of ditto 14 „ 6 „ 



As the other dimensions show the same ratio in botli skulls, we 

 find the cavity of the mouth in the Horn-frog nearly four times 

 as spacious as in the other. The teeth cannot have more than 

 a subordinate office in holding the struggling animals : as they 

 are present in the upper jaw only, relatively short, and not 

 hook-like, as in the Snakes, they would be of no use at all but 

 for the mandibula, by which an object may be pressed so firmly 

 against the series of teeth, that, as Tilesius relates, deep impres- 

 sions were found on a pencil seized by the animal. Thus the 

 principal efiect in holding the prey is produced by the muscular 

 strength of the mandible (together with that important cooperation 

 of the tongue common to all the Anura). Received in the cavity 

 of the mouth, the prey is unable to overcome the strength of 

 the elevators of the mandible ; consequently we find especially 

 those parts of the skull which serve for the insertion of these 

 muscles exceedingly developed and powerful, viz. the tympanic 

 and the neighbouring bones. Further to support the weight of 

 the skull and to afibrd a strong base for its muscular functions, 

 the hinder portion is furnished with strong crests and processes 

 for the muscles of the neck. The skull of Ceratophrys, com- 

 pared with that of other Anura, is modified in the same way as 

 that of a Carnivorous Mammal from that of an Herbivorous. 

 There we find a strong zygomatic arch and an elevated parietal 

 crest — here the tympanic bone and the front part of the occipital 

 crest are adapted to the same purpose ; there we have the hinder 

 portion of the skull elevated by the crest of the occipital bone 

 alone — here by a broad process of the os petrosum besides. 



Moreover, the other parts of the skull, which are not in im- 

 mediate relation with the process of feeding, are necessarily like- 

 wise strengthened, and form a striking contrast with the same 

 parts in other Anura, where portions of the bones remain carti- 

 laginous through life, or are thin, flexible, and joined together 

 only by a fibrous tissue, which may easily be destroyed. This 

 great strength of the bones in Ceratophrys is caused not only by 

 an* increased deposition of inorganic matter in the bones them- 



