RATHKE ON THE DEVELOPMENT OE THE CRANIUM. 
245 
angle a nearly horizontal thin plate or ala, which also chondrifies, 
and after a time appears convex on the upper, concave on the lower, 
side and covers the olfactory membrane more or less completely. 
Close upon these newly arisen horizontal cartilaginous plates, how¬ 
ever, which can also be recognized in perfectly adult animals, the 
nasal bones are formed. 
Another, but azygos bone is formed in Mammalia on the lower 
edge of the cartilaginous nasal septum, and in fact between the carti¬ 
lage itself and its perichondrium. This is the vomer, which, at first, in 
all cases, forms a simple grooved bone, in whose channel the nasal 
septum lies, just as in Birds the original cartilaginous orbital septum 
lies upon the presphenoid. # 
Such a bone is formed in this place in many Birds. On the other 
hand, in Amphibia and Beptilia a vomer never appears. The bones 
which have been regarded as such have a totally different nature. 
Immediately in front of the coalesced part of the trabeculae, finally, 
between the cornua into which it is produced, the premaxilla is formed 
distinct from those cartilaginous parts. In the Snake it is from the 
beginning single, but in other Vertebrata it originally consists of two 
symmetrical halves. 
/. With respect to the cartilaginous and bony parts of the olfac¬ 
tory apparatus, my investigations have yielded the following results. 
The cartilaginous septum narium, which has arisen by the coalescence 
of the anterior parts of the trabeculae, very early sends out from its 
upper edge, as has been already stated, a plate which curves round 
the upper side of the olfactory sac. It attains its smallest volume, 
among those animals which stand above the Batrachia, in the Snakes; 
the largest, in Mammalia. In the Beptilia it arches only over the 
upper side, in Birds and Mammals also round the outer side, of the 
olfactory sac. A part of it is developed in many Birds, ( e . g. Gralli- 
nacese) into the cartilaginous squama which covers the nasal aperture, 
in Mammalia into the cartilaginous rudiment of an ala nasi. Further¬ 
more, in many of the Yertebrata above the Batrachia, it sends in, 
towards the cavity which is invested by the olfactory membrane, 
lamellar outgrowths, in greater or smaller numbers, which lie in folds 
of that membrane and form the turbinals.f Besides this, in Mam¬ 
malia, a part of this plate applies itself in front of the exit of the 
olfactory nerves from the cranial cavity, and forms the basis of one 
* The origin of the vomer and of the presphenoid between a cartilage and its 
perichondrium is otherwise remarkable, because, often when a destroyed bone is to 
be reproduced, the development of bone proceeds from the periosteum. 
f In my Essay on the Development of the Olfactory Organs of Mammalia 
(Abhandlung z. Bildungs- und Entwickelungs-Geschiclite d. Thiere), the origin of 
the turbinal bones from the two cartilaginous plates, which proceed from the septum 
narium was described at length. In a very large exotic Frog (liana ocellata ) I 
observed, that the large bony turbinal, which occurs in this animal, was developed 
not from the upper, but from the lower plate of the nasal septum, which is united 
with the oalatine bones and is peculiar to Batrachia. 
