242 
ORIGINAL ARTICLES. 
The pre-sphenoid is developed from a cartilage which is no longer 
a part of the investing mass of the notochord, hut arises quite inde¬ 
pendently of it. 
In the Snake, this cartilage is developed within the mucous 
tissue (S'chleimstoff") which fills the long gap left by the non- 
coalesced trabeculae cranii, and it assumes a form corresponding 
with that of the gap, being a narrow, moderately thick, anteriorly 
pointed, and altogether almost stilet-shaped body. When it has 
ossified, however, its posterior end grows broader, and changes into 
a little plate, which, growing towards and abutting against, the 
margin of the basisphenoid, eventually coalesces with it. When this 
has taken place, the presphenoid appears partly as a spine, into 
which the basis cranii passes anteriorly. Tor the rest, in the Snake, 
the posterior parts of the trabeculae cranii, between which the pre¬ 
sphenoid arises, increase not a little in length and thickness, and 
remain recognizable, throughout life, as two rounded cartilaginous 
spines converging anteriorly, lying close on each side of the pre¬ 
sphenoid and passing immediately from the basisphenoid. 
In the Blindworm, the development of the basis cranii takes place, 
on the whole, as in the Snake. In the Lizard, in which the trabeculae 
cranii very soon coalesce throughout almost their whole length, the 
presphenoid is formed, not, as in the Snake, in the gap which remains 
between these trabeculae, but before it and at its under side, or rather 
along the lower edge of the cartilaginous orbital septum, which has 
become developed out of the coalesced parts of the trabeculae. The 
reason of this probably is, that, in the Lizard, at the time when that 
bone arises, the gap in question is very short and lies only quite 
posteriorly under the pituitary body. The form, again, which the 
body of the presphenoid assumes in the Lizard is different from that 
in the Snake; for, in the former, it is a narrow and very thin bony 
lamella, which, it may be remarked in passing, is lost with the septum 
when the skull is macerated too long. 
Although, now, the presphenoid of Snakes and Lizards, as regards 
its position and form, arises in a somewhat different manner; yet, in 
all, its mode of origin is far more different from that of an ordinary 
vertebra, than that of the basisphenoid, and, in fact, is quite distinct; 
since, on the one hand, the presphenoid has no such relation to the 
notochord and its investing mass, as has the body of a vertebra; 
while, on the other hand, it has, from the beginning, a form altogether 
distinct from that of a vertebral body. 
In the Towl, the bones which constitute the floor of the brain- 
case are developed essentially in the same way as in the Lizard. The 
presphenoid arises also at the lower margin of the cartilaginous 
septum, which separates the eyes, in front of the gap which has per¬ 
sisted below the hypophysis cerebri and between the paired tra¬ 
beculae, and has, at first, the form of a moderately long, narrow, and 
thin grooved plate, in which that septum as it were rests. Soon, 
however, it becomes thicker, elongates further backwards, coalesces 
