DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 109 
(al.n., e.n.) already described, that the double nasal canal, after narrowing in a little, 
enlarges only gradually in the aliseptal region (a/.sp.). But in the aliethmoidal («l.e.) 
or proper olfactory territory it widens out rapidly, and forms a large bulbous structure 
which reaches backwards to the anterior sphenoid (0.s., p.s.). This broad end of the 
pyriform labyrinth is not finished by cartilage below, and the internasal desmos which 
binds side to side is the main vomer (v.). But the septal region, above the front 
half of the hard palate, and which is supplied by the ophthalmic or orbitonasal 
branch of the 5th nerve, is open, now that the lower bony floor has been removed. 
The thick base of the alinasal region behind the crescentic groove soon opens out, 
right and left, like curtains folded back, and the aliseptal wall behind the snout, for 
an extent which is half the length of the whole labyrinth, turns inwards very little 
below. This open part is divided into two lanceolate spaces by the septum nasi (above 
v’.), and its grooved bony rest—the vomer (v., see also Plate 14, tig. 5). 
But the nasal canals are not open towards the hard palate more than by narrow 
chinks ; for there are two pairs of folded eartilages in this general open space—two on 
each side—one, the internal, half the size of the other, the external, fold. 
From above the inner part of the selvedge of the closed floor of the snout, close 
to the septum nasi, right and left, a rod of cartilage—the recurrent cartilage or the 
cartilage of JACcOBSON’s organ—grows backwards, and before it passes inside the 
opening of that organ (j.0.) it sends a curling process half way round the front of the 
passage. The narrow stem, beyond the opening of the organ, soon expands, and then 
the cartilage becomes lanceolate, and ends opposite the middle of the outer coil, or 
inferior turbinal (7.tb.). Below, the recurrent cartilage is convex ; seen from the side 
(Plate 15, fig. 3, 7¢.c.), it is seen to be scooped on its supero-external face, The inferior 
turbinal arises opposite the thickening part of the lesser tract ; it also has the same 
lanceolate form with a convex under face, like the other, but is twice as large. This 
“maxillary,” or “inferior, turbinal ” is not fixed by its fore end ; its root is from the side ; 
it is an ingrowth of the aliseptal wall (a/.sp.). The thin lamina which grows inwards 
is concave below, it runs half-way across the gap in the floor towards the vomer, 
and then forms an upper and a lower secondary fold, These are coiled over from their 
common free face, like the leaflets of Cycas revoluta, but to a greater extent, 
The nasal turbinals cannot be seen in this figure; they are similar in all the 
Edentata, and dip down from the cartilage that underlies the nasal bones, just as the 
inferior turbinals grow in from the cartilage that lines the maxillaries (see in 
Tatusia, Plate 3, figs. 9 and 10, n.tb.). In the figures just referred to, and in 
figures, soon to be described, of these parts in the Hedgehog, a free section of cartilage 
is seen right and left of the septum nasi (s.7., pe.c.). They are a little displaced by 
the razor, and should lie nearer the base of the septum. This dissection of the nasal 
labyrinth of the Aard-Vark gave me the interpretation of those sections of the 
nose of Tutusia and Erinaceus. 
The lanceolate form of the gap right and left of the septum (Plate 14, fig. 5, and 
5 
