403 



tremity of the cornu of the hyoid. The hyoid and the mandibular 

 arches are thus suspended to the skull by a common peduncle, which, 

 to avoid all theoretical suggestion, I will simply term the " suspen- 

 sorium." 



The extent of the ossification which takes place, in and about this 

 primitively cartilaginous suspensorium, varies greatly in different 

 genera of Amphibia. Sometimes its distal end remains wholly unos- 

 sified ; sometimes, as in the common frog, a small outer portion 

 of its lower extremity is ossified and sends a process forwards, be- 

 coming what is termed the quadratojugal bone ; sometimes, as in 

 the Triton, the distal half of the cartilage becomes more or less com- 

 pletely enclosed in a bony mass. 



Another ossific deposit usually takes place in the outer half of the 

 proximal end of the suspensorium, extending for a greater or less 

 distance down towards the distal end, which it may even completely 

 reach. It may be a simple triangular plate, as in Triton, or a 

 T-shaped bone, as in Rana. In either case its lower end is the nar- 

 rower, and fits into a kind of groove in the posterior and outer 

 margin of the distal ossification. 



This bone was considered by Cuvier to be the equivalent of the 

 tympanic and the temporal (=squamosal) ; by Duges it was called 

 " temporomastoid." 



The last constituent of this region of the skull in the Amphibia is 

 one which is frequently overlooked altogether. In the frog, the 

 membrana tympani is supported by a well-defined cartilaginous and 

 partially ossified hoop, which is originally quite distinct from any of 

 the elements of the suspensorium which have just been described, 

 and which clearly deprives any of them of the right of being con- 

 sidered the homologue of the " tympanicum " of Mammalia. 



I must defer the attempt to decide what the parts of the suspenso- 

 rium really are, until the Piscine skull has been under consideration. 



Composition of the Skull of the Carp. 



The skulls of fishes present difficulties which necessitate, even for 

 my present limited purpose, the entering into greater detail regarding 

 them, than respecting those of the Reptilia or Amphibia. I select 

 the cranium of the carp for description, as it departs far less widely 

 from the common plan, and therefore forms a better type for com- 



