74 THE COMMON FROG. [chap. 



and can we, as it were, reach beasts by a short cut 

 through Batrachians, leaving all the reptiles and birds 

 on one side, as a special outstanding and diverging 

 developement ? 



We shall presently see that other yet more striking 

 facts may be brought forward in support of the latter 

 view. Nevertheless it must be remembered that there 

 are fishes, though very few and exceptional, which 

 also possess a pair of occipital condyles, and that in 

 one respect most fishes are more like mammals than 

 are any Batrachians, since they, like mammals, have a 

 well-ossified median bone at the base of the skull in 

 the occipital region, a structure which all Batrachians, 

 without a single exception, are destitute of. 



The second point of interest concerns the lower part, 

 or base, of the skull, which exhibits a striking agree- 

 ment with the same part as developed in bony fishes. 



This agreement consists in the fact that the middle 

 of the floor of the skull is not formed as in all beasts, 

 birds, and reptiles, b)^ a deposition of bony substance 

 in pre-existing gristle (ossification of cartilage), to 

 which the name Basi-sphcnoid is applied, but, as in 

 bony fishes, by a great bone called Parasphenoid^ 

 which shoots forwards and also extends backwards 

 to the hinder end of the skull floor, but is formed 

 by the decomposition of bony substance in pre- 

 existing membrane. 



Although this great membrane bone is constant in 

 Batrachians and bony fishes, and is represented, if at 

 all, only by minute rudiments in higher vertebrates ; 

 nevertheless in serpents we once more meet with a 

 far-reaching and well-developed parasphenoid. 



