732 B. W. KUNKEL 



becomes shallower in front; and the fenestra basalis is brought 

 well below the ventral margin of the septum, the upper side of 

 the fenestra standing at the level of the ventral margin of the 

 septum (figs. 9 and 27). 



The contour of the walls of the capsule follows closely that of 

 the underlying olfactory sac. Accordingly the capsule may be 

 differentiated into two distmct regions, a relatively high, some- 

 what conical pars olfactoria situated dorsally, and a broader 

 cylindrical pars respiratoria, opening in front by the fenestra 

 narina and behind by the fenestra basahs. These two regions 

 are separated by a shallow groove which extends diagonally pos- 

 teriorly and ventrally and becomes more pronounced at its pos- 

 terior end. The depression causes the interior wall of the capsule 

 to be thrown up into a corresponding ridge which supports the 

 lateral ' Grenzfalte' of Seydel. 



Above the groove just described is a second depression in the 

 lateral wall of the capsule. It is somewhat shallower than the 

 first and appears only along the middle third of the capsule. It 

 is the external manifestation of a corresponding ridge in the inte- 

 rior of the capsule. The accompanying proniinent fold of the 

 nasal epithelium supported by the thickening of the lateral wall, 

 is evidently a rudimentary concha. It extends posteriorly as 

 far as the recessus ducti naso-pharyngei, which is immediately 

 ventral to it. In older embryos than that modelled, the concha 

 becomes much more prominent on the inner side of the paries 

 nasi (fig. 19). 



The planum antorbitale is a thin curved plate making up the 

 posterior and postero-dorsal wall of the capsule. It slopes rapidly 

 ventrally from its antero-dorsal end and passes with an even 

 curvature laterally and anteriorly into the paries nasi. In the 

 stage modelled it is separated medially from the septum nasi by 

 the fissura orbitonasalis so that it has a free margin which is 

 rolled inwardly to project into the cavity of the capsule, parallel 

 to the septum (fig. 12). The infolded margin is broadest in front; 

 behind it disappears entirely in the region of the fenestra basahs. 



The tectum nasi is short in an antero-posterior direction and 

 comparatively narrow from side to side. In front it falls sud- 



