OF THE SKULL IK LEPIDOSTEUS OSSEUS. 
453 
The huge so-called pituitary space (py.) is pyriform, has an indented outline behind, 
and is apiculate in front. The concave inner side of the basal bands embrace the 
notochord closely, and end behind in bevelled flaps ; in front, where the last narrowing 
of the notochord takes place, they end almost transversely, but give off from their 
outer edge the trabecular outgrowths. They are quite confluent, externally, with the 
well-chondrified auditory capsules (au.). In their broad, proximal part the trabeculae 
(tr.) are dilated, and are perforated by the internal carotid artery ; * thence they 
converge steadily as scarcely arcuate bands, only one-third as large as their parachordal 
roots (iv.). 
Their front confluent part is as long as their hinder separate part; and there the 
bands double their width, have a convex outline externally, and narrowing inwards at 
their extremity, are continuous then with the palato-quadrate bars (p-pp-)- The 
front margin of these four bands is crenate, with three convexities, the middle 
enlargement being the largest; this is not, however, formed by the trabeculae them¬ 
selves, but by a pyriform wedge of newer cartilage, which has developed between and 
above them. This new element is the intertrabecula (• i.tr .); in the last stage (Plate 30, 
fig. 3, i.tr.) it was merely composed of embryonic cartilage—a small, inconspicuous 
tract of tissue, lying between the dilated ends of the trabeculae (tr.). 
This new tract does not reach to the pituitary space, but already, in the upper view, 
can be seen projecting beyond the confluent paired bands (tr., p.pg.). The simple, 
ovoidal form of the auditory capsules (au.) is now lost, for the semi-circular canals 
(a.s.c., h.s.c., p.s.c.) have developed greatly, and they have given the form of their 
curves and swellings to the cartilaginous capsule. 
The floor of the sacculus is still largely membranous (fig. 7, au.f.); this circular fenestra 
is inside the centre of the floor; within, also, the capsule is not cartilaginous. 
Outside, the bulging of the horizontal canal (h.s.c.) has formed a rudiment of the 
“ tegmen tympani” (fig. 7); this, however, is simply used to form the large oblong 
concavity for the hyomandibular (Jim.), and never acquires any tympanic function. 
The large cranial nerves have free course over the basal plate, and in front of and 
behind the auditory capsules they have only membrane to pass through ; the space for 
these (Plate 30, figs. 7, 8, IX., X.) is seen to be very wide. 
From the front of the auditory capsule cartilage is creeping along the superorbital 
region (fig. 8, s.ob.) ; this new tract is styliform, and at present only reaches one-third 
of the distance to the end of the chondrocranium. Below this rudiment, right and 
left, of the “ tegmen cranii ” the proximal part of each trabecula has developed an 
oblong facet of cartilage for articulation with the pedicle of the suspensorium 
(pd) ; this is the first appearance of the paired “ basipterygoid ” processes of the basi- 
eranii. I take this to be not only the first appearance of these important processes in 
* This passage is seen inside the superorbital cartilage {s.ob.) ; the line leading from the letters to this 
part in fig. 8 is not long enough, 
