94 



Elementary Zoology. 



cranium is well seen by reason of the fact that they can without 

 much difficulty be stripped off. Roofing the skull above are a 

 pair of long bones, closely applied to each other in the middle 

 line ; these are the fronto-parietals. In front of these are the 

 two nasals partly concealing the olfactory orifice, and in front 

 of these, again, the small premaxillce. On each side of the skull, 

 in the auditory region, is a hammer-shaped squamosal. On the 

 under surface of the skull the most conspicuous of the membrane 

 bones is the large and dagger-shaped parasphenoid, of which 



P.M.X 



ST.HY 



BO 



Fig. 40.— Skull of Frog. Ventral aspect. (After W. K. Parker.) 



.palatine; eth, sphenethmoid; par.sp, parasphenoid ; E u> Eustachian 

 tube; QR, quadrate: st.hy, stylohyal. Behind pmx are vomens 

 (dotted), in front of which are internal nares. Other letters as in 

 Fig- 39- 



the " blade " underlies the greater part of the base of the skull. 

 In front of it, and bearing much the same relation to the internal 

 nares as the nasal do to the external nares, are the small vomers ; 

 to the side the maxilla. Laterally there is a splint of bone 

 forming the outer arcade of the skull, the quadrato-jtigaL 

 The skull, thus stripped of its membrane bones, is seen 'to be 

 chiefly cartilaginous, but with some ossifications. 



