298 
MU. W. K. PAEKEE ON THE STEUCTUEE AND 
coils. The bilobate mass directly above the trabecular horn ( al.tb ., i.tb., c.tr .) has its 
anterior lobe developed into the curious “ alinasal turbinals ” immediately within the 
snout, whilst its hinder lobe becomes the long “ inferior turbinal.” The swelling below 
the down-turned roof is the rudiment of the “ nasal turbinal,” scarcely developed in the 
adult of this type ; and the mass which lies beneath the rudiment of the olfactory crus 
(1) becomes the upper and middle turbinal (one mass in the Pig) and the true olfactory 
region. Vertical sections* show, most instructively, what could in nowise have been 
guessed at — namely, that the nasal labyrinth has its skeletal parts formed by the approxi- 
mation and coalescence of two imperfect cylinders open freely below, and by these 
receiving at their junction below the ascending crest formed by the conjugated trabeculae 
(Plate XXIX. figs. 1-3, al.s., al.e ., tr.). When these trabecular bands continue flat 
(as in the embryo, Plate XXIX. figs. 1 & 2, tr.), then we have, as in the Prog and the 
Crow, a cartilaginous floor to the nasal passages (see memoir on “ Prog’s Skull,” Plate vn. 
fig. 6, and Plate x. fig. 3, s.n.L ; and also Proc. Roy. Micr. Soc., Oct. 2, 1872, p. 224, 
pi. 38. fig. 1, s.n.). In most Mammals, and in Birds not belonging to the Passerine 
group, the trabeculae narrow in to form the rounded thickened base of the whole “ ethmo- 
presphenoidal bar this process is seen to be beginning in the section through the 
posterior part of the nasal region (Plate XXIX. fig. 3, tr.). The section through the 
inner nares (Plate XXIX. fig. 3, i.n.) also shows the back wall of each nasal passage 
(p.n.w.). These large rounded spaces are seen to have the rudiments of the last of the 
middle turbinal coils already continuous with the end wall. These posterior walls 
correspond to the end of each “ sphenoidal sinus this is therefore the presphenoidal 
region, and behind the mesoethmoid ; and the pyriform openings above were made 
through the front of the cranium and through the fore end of the cerebral hemi- 
spheres, where they bud-off the olfactory crus (see also Plate XXVIII. fig. 6, C 1“, ol.). 
This same section has cut through the first cleft (first preoral or lacrymal passage) on 
its way to the nasal passage. The anterior extremity of the, as yet, soft palato-pterygoid 
rod (ppg-) is here cut through, where it passes below the inner nostril [i.n.). The 
space between the rudimentary olfactory crus and the budding upper turbinal (Plate 
XXVIII. fig. 6, ol., s.n.) is composed, at present, of an almost structureless gelatinous 
stroma ; it is slow to form those cartilaginous bands afterwards, which, creeping between 
the olfactory filaments, form the cribriform plate — a secondary morphological structure 
almost entirely peculiar to the Mammalian skull. 
The eyeball only affects the skull from without, by modifying the facial and cranial 
structures to form its safe recess or orbit ; but the earball is constructed after the 
fashion of the old cottage oven, being built into the side walls of the skull, bulging out 
on the outside, and having its nerve-mouth projecting also within. 
In my last paper, on the Salmon’s skull, I was able to show the infolding of the 
* These vertical sections of the nasal region were made by the same slicing as the horizontal sections of the 
head further back : this depended upon the hooked shape of the head at this stage ; the razor passed at right 
angles to the nasal roof, but parallel to the notochord. 
