240 
ORIGINAL ARTICLES. 
less thick plate, which afterwards chondrifies, whilst that part of the 
chorda itself, sooner or later, disappears, without leaving a trace 
behind. This disappearance takes place soonest in the Mammalia, 
latest in the scaly Amphibia. From the plate in question pass three 
trabeculae, at first consisting of condensed blastema, afterwards of 
cartilage, which are proportionally very thick. 
The azygos one which passes upwards, and is situated in the in¬ 
terspace between the anterior and the posterior cerebral vesicles, in 
time disappears altogether; for the posterior clinoid processes of the 
sella turcica, which are found in the higher animals, only take its place 
and are not developed out of it. The paired trabeculae cranii extend 
at once to the lower part of the primitive wall of the forehead, out of 
which gradually the so-called frontal process of the head (a part of the 
face) is developed, and here they are closely approximated; in the 
rest of their course, however, they are more or less widely sepa¬ 
rated. Of this, one may convince oneself by the examination of 
embryos of the animals mentioned above, even of Mammalia, while 
they still possess branchial clefts. Between the trabeculae the basis 
cranii is very much thinner, and its texture is not so granular; and, 
through the posterior part of this, or the gap of the basis cranii, as 
it might be called, the oral mucous membrane is protruded towards 
the cranial cavity to form the pituitary body. 
b. The further development of the basis cranii is different in the 
different animals which stand higher than the Batrachia. The two 
trabeculae, before they chondrify completely, approximate for a 
greater or less distance and coalesce. In the different higher 
animals, however, this happens for a greater or a less distance. In 
Mammals they unite very early throughout their whole length. In 
the chick there lies between them posteriorly, when the pituitary body 
has been formed (even after the feathers have begun to develope), 
a very large rounded gap, filled only by connective-tissue (Zellstoff). 
In the Lizard there exists at the same spot, even at the end of 
foetal life, a somewhat larger but triangular gap filled with connective- 
tissue. A still larger and elongated space of the same kind remains 
between the posterior parts of the trabeculae in the Blindworm up to 
the end of foetal life. 
Among the higher animals the cranial development of which I have 
examined, however, it remains longest and largest in the Snake; for 
in this animal it extends, even late in life, as far as the anterior end 
of the brain-case, though it is very narrow in its anterior half even 
in the middle of foetal life. 
Furthermore, the originally separate parts of the trabeculae become 
longer the greater the size attained by the eyes: these parts conse¬ 
quently remain shortest in Mammalia and are longest in Birds and 
Lizards. 
Yet another difference in their further development depends upon 
the extent to which the eyes increase in magnitude. If these acquire 
a considerable volume, as is especially the case in Birds and Lizards, 
