696 B. W. KUNKEL 



of more compact form on account of the shortening of the space 

 between the olfactory and otic capsules, the numerous fenestrae 

 of the lizard skull are reduced both in number and size. At the 

 same time also, the slender rods of the lizard's skull are to a great 

 extent replaced by broad, more or less continuous, plates. In this 

 respect the chelonian chondrocranium resembles more nearly 

 that of Sphenodon as described by Schauinsland ('00) and Howes 

 and Swinnerton ('01) and that of the crocodile described by 

 Parker ('83) than it does that of the lizards (Gaupp '00) and 

 snakes (Parker '78). The greater strength of the jaws of the adult 

 chelonian and crocodilian seems to be early foreshadowed in the 

 embryo by the greater solidity of the skull, especially in the por- 

 tions more intimately associated with the jaws. Notwithstand- 

 ing, however, this greater solidity of the chelonian chondrocra- 

 nium, in one respect it seems to be weaker in that it lacks the taenia 

 marginalis which couples the orbital region with the otic capsule 

 dorsally. In Emys the orbital and temporal regions are discon- 

 tinuous except for the trabeculae which lie near the mid-ventral 

 line, and the temporal and otic regions are discontinuous except 

 ventrally because of the absence of the taenia marginalis. More 

 detailed comparisons of the reptilian chondrocrania will be made 

 below, under the respective parts of the skull. 



PLANUM BASALE AND CHORDA DORSALIS 



The basal plate forms the entire floor of the parachordal portion 

 of the chondrocranium (fig. 25) extending forward from the occi- 

 pital condyle through the occipital and otic regions. It is simple 

 and continuous as far forward as the anterior half of the otic 

 capsule where the hexagonal fenestra basicranialis posterior is 

 situated. In front of this space the floor of the skull is rep- 

 resented by a heavy, transverse bar, the crista sellaris, which 

 forms the hinder boundary of the fenestra hypophyseos (f.h.). 



There can be but httle doubt that the part of the skull here 

 referred to as basal plate is made up in part, in the otic region, 

 from the floor of the otic capsule. In a- much younger stage 

 (carapace length, 4.7 mm.) the boundary between the blastema 

 of the basal plate and that of the otic capsule is quite distinct. 



