390 ROBERT J. TERRY 



paranasal cartilage forming a part of the primitive nasal floor 

 which, by reduction, came eventually to be represented by more 

 or less separate parts (Jacobson's cartilage) in the mammals. 

 In the light of this interpretation, the slender cartilaginous para- 

 septal strip which appears late in the development of the cat, 

 and unites Jacobson's cartilage with the posterior transverse 

 lamina, may be regarded as evidence of a partial restoration of 

 the primitive floor. 



Tectum nasi. Noordenbos has observed the beginning of the 

 tectum nasi in mole embryos of 9 mm. as bilateral divisions of 

 the anterior margin of the trabecular plate, forming curved 

 lamellae. In the dorsal middle line a shallow groove stands be- 

 tween the two halves of the tectum. In the cat the nasal tec- 

 tum arises apparently similarly in connection with the nasal 

 septum, as the parieto-tectal cartilages, although, as already 

 mentioned, some evidence of the independent origin of these car- 

 tilages was presented. The groove between them, dorsad of the 

 septum, is the beginning of the sulcus supraseptahs. In the 

 cat, the parieto-tectal cartilages gi-ow back, along the dorsal mar- 

 gin of the septal cartilage, as far as the fenestra olfactoria, becom- 

 ing gradually narrower from side to side and assuming the form 

 of triangular plates. These cartilages contribute the entire roof 

 of the pre cerebral division of the nose and the side wall anterior 

 to the recessus lateralis. What the relations of the parieto-tectal 

 are to the development of the lamina transversalis anterior were 

 not determined. Eventually a complete zona annularis is es- 

 tablished behind the level of the fenestra narina, the roof being 

 derived from the parieto-tectal cartilage, the floor from the 

 lamina transversalis anterior, the lateral wall from the union of 

 these two parts. The relations of the lateral margin of the parieto- 

 tectal with the anterior free margin of the paranasal cartilage are 

 at first similar to those in Talpa, as observed by Noordenbos. 

 This cartilage does not seem to be concerned in the formation of 

 the maxilloturbinal, although in the stage of 23.1 mm. this proc- 

 ess is connected with the anterior part of the lateral nasal wall 

 through the lamina supraconchalis. Within the nasal cavity the 

 atrioturbinal appears as the inrolled ventral margin of the 

 parietotectal cartilage. 



