PRIMORDIAL CRANIUM OF THE CAT 399 



20. A ca^iiin epiptericum and caviun supracochleare are recog- 

 nized in the chondrocranium of cat. The names 'membrana 

 hmitans' and 'septum transversum' are proposed for the mesen- 

 chymal • sheets connected with the walls of the orbito-temporal 

 region. In the cat the internal carotid artery enters the mem- 

 brana limitans, by the carotid foramen, and secondarily into the 

 primitive cranial cavity. A bar of cartilage in the septum trans- 

 versmii, lying upon the semilunar ganglion, is probably a vestige 

 of the primitive chondrocranial wall. 



21. The ala orbitaUs arises independently in the cat and 

 unites secondarily ^^dth the paranasal cartilage, orbitoparietal 

 commissure, and trabecular plate. It is apparently primarily 

 adapted to the eyeball and its adnexa. 



22. A region, extracranial in reptiles, is represented within 

 the chondrocranimn of cat as the supracribrous region of the 

 ethmoidal skeleton. 



23. The structm-e of the anterior part of the floor of the nose 

 is in agi'eement with the descriptions of Broom and Zucker- 

 ka-ndl. The nasopalatine cartilage of mammals is interpreted 

 as a structure originally distinct from the lateral posterior car- 

 tilage of the nasal floor, and its connection with the latter 

 secondary. 



24. Jacobson's cartilage in the cat is the anterior, well de- 

 veloped, portion of a paraseptal cartilage, connected posteriorly 

 with the lamina trans versaUs posterior. 



25. The cartilaginoUvS ethmoidal skeleton of the cat is sepa- 

 rated on developmental grounds and physiological relations, 

 into a small ventral part and a large dorsal part. The former 

 presents incomplete walls about the inferior meatus; the latter 

 rather continuous walls about the paranasal sinuses and olfactory 

 region of the nose. 



26. The dorsal part of the ethmoidal skeleton in embryos to the 

 stage of 30 mm. is formed from the septal cartilage, parieto-tectal 

 cartilages, paranasal cartilages and the laininae antorbitales. 



27. The parieto-tectal cartilages, paired, spring from the septal 

 cartilage. They contribute the roof of the precerebral division 

 of the ethmoidal skeleton, the side wall of the atrial region, 



