400 THE NASAL REGION IN EUTAENIA. 
with the mucous or lower nasal chamber, whose size is diminished 
by the mucous folds. The inner wall of the mucous chamber runs. 
into a tube prolonged forward on a level with the Organ of Jacobson, 
and ending blindly immediately behind it. The tube is succeeded 
by a groove of the same calibre, which, with its fellow of the opposite: 
side, narrows considerably the fleshy septum. The canal and groove 
are lined with folded mucous membrane. With the termination of 
the turbinal the passage becomes smailer and descends to the roof of 
the mouth to end in the choanae. These, observed from below, are 
slightly crescent-shaped, and are separated by folds (Fig. 1, chf.) 
which contain between them the choanal cul-de-sac, ending blindly in 
front over the middle palate. The choanal depression is somewhat 
narrowed below by a fold on each side from the palatine ridge. 
It is necessary to add some further details concerning the general’ 
histology of the nasal cavity, in addition to what is given above, for 
one section of it. 
In the groove in the floor of its cavity, in front of the nasal open- 
ing, the cells of the lining membrane are, passing from its base 
upward, oval and granular, then large and polyhedral, and covered by 
a layer of flat corneous cells, the latter several layers thick near the 
posterior termination of the groove. The whole offers no contrast to: 
that found just inside the lips, except in the size of its constituent 
cells. 
The cavity anteriorly to the Organ of Jacobson is very poor in 
olfactory epithelium. The mucous membrane is but little folded, 
and the cylindrical cells with thick cilia appear to wander into the 
olfactory portion. 
Above the Organ of Jacobson the mucous folds of the lower 
chamber seem to fill it out completely, while the olfactory epithelium 
does not reach that development which obtains behind. For there 
the turbinal is of its greatest transverse length, and its rounded edge, 
like the inner and upper walls of the upper nasal chamber, is lined 
by well developed olfactory membrane. The superficial and sen- 
sory portions of the same are wanting in the floor of the upper 
chamber. Coincident with the disappearance of the turbinal 
behind, the olfactory epithelium becomes scanty again, and on 
the roof and floor of the passage, in the immediate neighbor- 
hood of the choana, is replaced by mucous membrane, that lining 
the roof abounding in goblet cells, while the majority of the 
