I.] THE FROG. 63 



There will thus be laid bare the chondro-cranium and 

 its related bones. 



a. Dorsal aspect. 



a. The chondro-cranium; a cartilaginous mass en- 

 closing the brain and olfactory and auditory 

 sense organs, and bearing, laterally, an out- 

 standing cartilage which is flanked by the pala- 

 tine and pterygoid bones (palato-quadrate car- 

 tilage or sub-ocular arch). 



/?. The sphenethmoid, pro-otics and exoccipitals ; seen 

 to be formed as replacements of the chondro- 

 cranium in bone; they are inseparable from it, 

 being termed therefore cartilage bones, by way of 

 distinction from those superadded ones which 

 have been stripped off (membrane bones). 



Examine in detail. 



y. The cranium ; its roof will be seen to be in- 

 completely cartilaginous, bearing three mem- 

 branous areas or fontanelles, all of which un- 

 derlie the fronto-parietals. They are a larger 

 median one in front, extending forwards to the 

 posterior border of the sphenethmoid ; smaller 

 paired ones behind, extending outwards to the 

 inner border of the pro-otics. 



3. The sub-ocular arch; confluent, in front with 

 the olfactory capsule, behind with the auditory 

 capsule, \\spalatinebar; standing out at right 

 angles to the long axis, and expanded ex- 

 ternally to form a plate (orbital process) for sup- 

 port of the maxilla (cf. opposite side). Its 

 pterygoid bar ; produced backwards, outwards 



