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}. 



ft. 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. 



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

 the olfactory capsule, behind with the auditory 

 capsule. Its palatine bar ; 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 



