246 
ORIGINAL ARTICLES. 
lateral half of the lamina cribrosa of the ethmoid, while in Birds and 
Beptiles this is not the case. 
At certain points of the two plates of the nasal septum in ques¬ 
tion, the gelatinous substance of which they originally consist, is 
not chondrified, but becomes membranous. Of the cartilaginous mass 
of these plates, however, certain parts become changed, especially in 
Mammals, into bone, and are further developed into the olfactory 
turbinals, the lamina cribrosa and the lamina papyracea of the 
ethmoid. # The septum itself which sends out the plates also partly 
ossifies in Mammals, and this, its ossified moiety, then appears as the 
bony part of the nasal septum, together with the crista galli, the 
foundation of which last had been laid by a prolongation of the ori¬ 
ginally merely cartilaginous septum. 
On the other hand, this septum does not ossify in the Beptilia, nor, 
as a rule, in Birds, but remains permanently cartilaginous in them. 
In Birds, however, at the end of foetal life, at least the anterior 
part of the cartilaginous orbital septum, which is continuous with the 
septum narium, ossifies. The osseous plate, which is thus produced, 
and which is commonly regarded as a part analogous to the ethmoid 
of Mammals, coalesces in most Birds with the anterior half of the body 
of the sphenoid. 
The premaxillse arise, as was before mentioned, between the two 
cornua, into which the external part of the paired trabeculae is 
produced anteriorly. If the horizontal part of the premaxillse, 
which grows towards the maxillae, acquires a considerable size it 
applies itself to the under surface of those cornua, which at the 
time when the nasal septum is developed proceed from its lower 
marginal portion. The cornua in question are found even in 
adult animals, especially in Buminants, the Horse, and many other 
Mammals, t 
§ 14. In the larvae of Rana viridis and Rana temporctria , the 
cephalic part of the notochord extends, also, only to between the 
auditory organs—tapers but very little however, and ends by a very 
short point. The investing mass forms a broad and moderately 
thick plate, which projects beyond it, forwards, almost to the pituitary 
body, and remains merely cartilaginous up to the very end of larval 
life. In larvae whose hind legs have but just budded, this cartila¬ 
ginous plate has only a small thickness; sends upwards, behind ihe 
auditory capsules, two small processes (the lateral parts of the 
occipital bone) and is continued forwards into two, also very thin, 
cartilaginous bands or trabeculae. The two latter are tolerably broad 
and are separated by an oblong gap which is much broader than 
either. The gap is filled up by a very delicate membrane which ap- 
* Hence it follows that the capsules which in the Snakes inclose the nasal glands 
cannot be the equivalents of the ethmoids of other animals. 
t.1 have given figures of these parts in the Snake in my account of the develop¬ 
ment of this animal. 
