THE AMPHIBIAN SKULL. 



153 



other Vertehrata. Turbinal ossifications are developed in the 

 cartilage bounding the nasal capsules in some Ampliibia, 



Pm 



z qj-\ 



Pmx, 



Fig. 55. — Skull of Rana esculenta. A. from above; B, from below ; C. from the left sido 

 cc, parasphenoid ; y, girdle-bone ; Z, the " teujporo-mastoid." 



The membrane bones of the Amphibian skull are : 1. Front- 

 als and parietals, which, in the BatracJiia^ may be fused to- 

 gether into one bone. 2. Nasals are generally present. 3. 

 The vomers, always present, are two in number, one for each 

 side, in all Amphibia but Pipa^ Dactylethra^ and Pelobates, 



4. A great parasphenoid covers the base of the skull from the 

 occipital to the ethmoidal region, as in TeUostei and Ganoidei, 



5. A membrane bone (Z), called " temporo-mastoid " by Du- 

 ges, lies on the outer side of the suspensorium, extending from 

 the side-walls of the skull to the articular head for the lower 

 jaw. The relations of this bone in its upper part are similar 

 to those of the squamosal of the higher Vertehrata., in its lower 

 part to those of the bone F in Lepidodren., to the preopercu- 

 lum of fishes, and to the tympanic of the higher Vertehrata, 



Two premaxillae are always developed. The maxillae are 

 usually present, and may be connected, as in most J3atrac7iia, 

 by quadrato-jugal ossifications with the outer side of the end 

 of the suspensorium, in which an ossification representing the 



