244 
ORIGINAL ARTICLES. 
Solipedes, and Rodents; but further investigations are required for 
the clearing up of this point. 
d. The exoccipitals certainly arise in the Reptilia, Birds and 
Mammals, in just the same manner as the neural arches of the ver¬ 
tebrae : in fact they appear not merely in their gelatinous, but also in 
their cartilaginous condition, as radiations from the investing mass of 
the cephalic part of the notochord. Indeed, in many animals, viz. 
Snakes, Lizards and the Blindworm, their upper ends even, like 
those of the neural arches of a vertebra, come into contact with one 
another, and then coalesce. In those higher Yertebrata however, 
in which the brain attains a greater volume, they do not meet, and 
there is developed between them a special os intercalare, the supra 
occipital. 
On the contrary the ali- and orbito-sphenoids never arise by the 
outgrowth of chondrified parts of the basis cranii; for they grow 
neither out of the trabeculae, above which they appear, nor out of the 
basi- or pre-sphenoids, when these different parts are in the cartila¬ 
ginous Condition; but they are formed separately in the originally 
gelatinous lateral walls of the brain case. 
In Lizards the alisphenoid appears at best only as a thin bony 
plate, (the columella of Cuvier) and the orbito- sphenoid is entirely 
wanting, whence, in these animals, that half of the lateral walls of the 
brain case which lies in front of the petrosals remains almost entirely 
membranous. 
Neither in Birds are any separate orbito-sphenoids formed. On the 
other hand, the frontals, as they increase in size, abut against the car¬ 
tilaginous orbital septum and then coalesce with it, when at the end 
of foetal life it ossifies, as I shall show below. 
e. I have stated above that the paired trabeculae cranii, in those 
animals which are above the Batrachia, meet anteriorly at a very 
early period and then separate again, forming two little cornua. This 
anterior coalesced part, with its cornua, lies where the lower wall of 
the capsule which now invests the brain and which will become the 
cranium, passes into the anterior, or the frontal wall—at the spot, in 
fact, where the so-called frontal process of the head, a part of the 
face, is developing. On both sides of the most anterior part of the 
trabeculae, and in fact close behind their cornua, the olfactory sacs 
are formed. Whilst these increase in size, the paired trabeculae of the 
skull coalesce between them, become cartilaginous and grow into a 
plate the length and height of which correspond with those of the 
olfactory organs of the animal. This plate is the nasal septum. 
In those animals, in which, from a similarly coalesced part of the 
paired trabeculae cranii, an interorbital septum has also been formed, 
viz. in Lizards and Birds, the two septa pass uninterruptedly into 
one another, so that the one may be regarded as a continuation of 
the other, or rather, the two make one whole. 
Prom each side of the upper edge of the septum narium there 
grows out very early (even before it chondrifies), at almost a right 
