PRIMORDIAL CRANIUM OP THE CAT 331 



there are ^wo on each side. In its ventral one-third the groove 

 is broad and shallow and adjoins the anterior region of the paries 

 nasi and the lateral prominence. It occupies an area which 

 passes ventrally into the maxilloturbinal and stands at a level an- 

 terior to the crista semicircularis. This part of the paries navsi 

 corresponds to the lamina supraconchalis of Voit. The second 

 groove, sulcus lateralis posterior, limits the lateral prominence 

 posteriorly; it is broad and shallow and stands opposite ethmo- 

 turbinal I within the capsule. The anterior region of the par- 

 ies nasi extends from the antero-lateral sulcus to the lateral mar- 

 gin of the fenestra narina. It is co-extensive with the roof dor- 

 sally, but becomes narrow ventrally where it joins the lamina 

 transversalis anterior. The surface in this region is convex, 

 corresponding to the internal concavity of this part of the lateral 

 wall. The middle region, the prominentia lateralis, is narrow 

 from before backward. Dorsally it is united with the commis- 

 sura spheno-ethmoidahs and forms the lateral boundary of the 

 olfactory window, between the posterior extremities of the crista 

 semicircularis and ethmoturbinal I (vide infra). Ventrally it 

 passes into the maxillo-turbinal. The posterior area, antorbital 

 plane, corresponds to the region within occupied by the ethmo- 

 turbinals, and forms the antero-medial wall of the orbit. Where 

 it adjoins the middle region of the paries nasi (sulcus lateralis 

 posterior) there is present ventrally a rounded prominence, giv- 

 ing origin to the inferior oblique muscle of the eye. The dorsal 

 margin of the antorbital plane at the orbito-nasal fissure, partici- 

 pates, anteriorly in the lateral boundary of the olfactory window, 

 and posteriorly passes into the lamina infracribrosa. The ven- 

 tral margin is straight and free in the lateral boundary of the 

 fenestra basalis. Caudally, this division of the nasal capsular 

 wall continues into the posterior cupola. This conical shell ex- 

 tends backward at the side of the nasal septum and trabecular 

 plate beneath the preoptic root of the ala orbitalis. It is closed 

 ventrally by the lamina transversalis posterior, which reaches to 

 the septum nasi. The roof of the posterior cupola is formed by 

 the unpaired lamina infracribrosa (figs. 1, 25). This plate pre- 

 sents a free edge anteriorly toward the fenestra olfactoria, con- 



