PRIMORDIAL CRANIUM OF THE. CAT 391 



Paranasal cartilage. Independent origin of a plate of carti- 

 lage lying in the anterior part of the lateral wall of the nose has 

 been observed by Noordenbos in embryos of Talpa of 9 mm. 

 length; also in the embryos of calf and pig. Following Mihal- 

 kovics, the cartilage was called cartilago paranasalis. In Talpa, 

 the paranasal cartilage and the tectmn nasi are separated by a 

 fissm-e, bounded by the anterior border of the former and the 

 free margin of the latter. In the cat, also, an independent para- 

 nasal cartilage occurs which bears similar relations to the parieto- 

 tectal cartilage. It is directly over that diverticulum of the 

 cavum nasi which later is included in the recessus lateralis of the 

 ethmoidal skeleton. The little cartilaginous plate, bent upon 

 the convex bulging of the nasal sac, presents free margins: one 

 toward the side of the olfactory lobe; one backward toward the 

 eye; a ventral margin, and a long anterior side, opposite the free, 

 oblique edge of the parieto-tectal cartilage ; relations comparable 

 with those observed in the mole. 



Great interest attaches to the ventral and anterior margins of 

 the paranasal cartilage. The latter overlaps the parieto-tectal, 

 and, whereas in younger embryos it is separated from that car- 

 tilage by a fissur'e, it is later fused with it. The result of this 

 fusion is a curved, intranasal ridge, the crista semicircularis, per- 

 forated by the foramen epiphaniale, which is the remains of the 

 original fissure. Thus is explained the position and extent, quite 

 to the olfactory fenestra, of the semicircular crest. It follows 

 from its mode of formation that, in later stages, the crista semi- 

 circularis may be taken as the boundary between two originally 

 distinct territories of the nasal wall. During the period occupied 

 by the process of fusion of the incurved anterior margin of the para- 

 nasal and the hinder margin of the parieto-tectal cartilage, and 

 for some time thereafter, an interval of variable extent (derived 

 from the space of the original separating fissure) is enclosed 

 within the encompassing cartilaginous margins; that is, for a 

 time the crista semicircularis presents double walls with an inter- 

 vening space; this space is crossed by the lateral nasal nerve at 

 the level of the future epiphanial foramen. 



