PRIMORDIAL CRANIUM OF THE CAT 395 



terest is the relation of the antorbital plate to the ethmoturbinal 

 bodies. A well developed, epithehal ethmotui'binal fold can be 

 seen behind the recessus laterahs in embryos of 15 to 17 mm. 

 We have seen that the posterior margin of the paranasal carti- 

 lage overlaps the anterior edge of the antorbital plate, and that 

 the latter projects forward and medial ward into the base of the 

 epithehal fold of ethmoturbinal I. Sections show that the an- 

 terior, free cartilaginous extremity of this ethmoturbinal, in 

 embryos of 23.1 mm., is formed, in connection with mesenchyma, 

 within the fold of epithelium and independently of the wall of 

 the nasal capsule. The mesenchyma can be followed, however, 

 backward to the base of the fold and to the ridge of cartilage 

 derived from the antorbital plate of earher stages, which 

 bounds posteriorly the opening into the recessus laterahs. 



The development of the ethmoidal skeleton in the cat indicates 

 a certain degree of correlation between its cartilaginous com- 

 ponents and regions of the nose more or less sharply defined by 

 particular functions. The dorsal, larger, and more completely 

 walled division includes the olfactory and paranasal territories 

 and the atrimn opening toward them; whereas the ventral, 

 smaller and imperfectly formed division stands in relation to 

 the respiratory air passage, nasopalatine and lacrimal ducts. 

 Even the original components of the dorsal division present evi- 

 dence of specific adaptation to functional territories. Thus, the 

 antorbital plate forms the wall of the ethmoturbinal territory 

 of distribution of the olfactory nerve, the paranasal cartilage in- 

 closes the diverticulum of the lateral recess, later the frontal 

 sinus; and the parieto-tectal develops into the wall of the atrimn. 

 I do not wish to imply that the evidence at hand justifies the 

 conclusion of rigorous specificity of these components, it cer- 

 tainly does not; but facts are sufficient to indicate that each of 

 these original cartilages is, in the main, developed in relation 

 to recognized functional territories of the nose. 



