482 
MR. W. K. PARKER OK THE DEVELOPMENT 
This is a very feeble rudiment of the thick and high wall, which is developed in this 
part in most of the “ Amniota,” where it runs up in the deep fissure under the mid 
brain. However, even here it divides the basi-cranial fontanelle into two parts, a 
large anterior (py.) and a small posterior space (qo.b.cf.). 
Thus it is evident that in this, as in other kinds of Ichthyopsida, the basis-cranii 
is much less affected by the mesocephalic flexure than it is in the Sauropsida and 
Mammalia. 
The main pituitary space (Plate 38, fig. 3, py.) is lessened by the ingrowth of the 
trabeculae itr.) ; but in front, it is filled in by the hind part of the long intertrabecula. 
The trabeculae are bowed out right and left, between the 5th and 2nd nerves (V., II.); 
the 1st nerve (I.) escapes from the front of the enclosed end of the cranium, and runs 
all the distance to the nasal sacs close to the sides of the intertrabecula ( i.tr.) 
The paired trabeculae (tr.) do not end where the skull has closed in; in front of the 
narrowed tegmen cranii (Plate 38, figs. 1, 2, t.cr.) the intertrabecula is seen to be narrow 
above, and to have narrow wings running along its sides. 
These wings soon dilate, so as to give the rostral part of the skull an oval widening 
along the front two-fifths of its hinder fifth . These parts are the cornua trabeculae, 
and although they are so short now, they were (Plate 30), once, the main part of the 
skull in front, and for some time came little short of the end of the snout. Now, they 
are like the right and left sides of a lanceolate leaf, with a huge mid-rib; only their 
terminal point is free, and the 1st nerve runs in a groove between them and the long 
rostrum. 
The rostrum (i.tr.) is very uniform up to near the front end; it then becomes 
slightly alate before ending in a blunt and somewhat decurved point (p.n.) ; its 
section is nearly oval, the thicker end below. 
The suspensorium (Plate 37, fig. 4, and Plate 38, fig. 5) retains the form it had 
in the last stage (Plate 34), but it is twice as large, and its bony centres are now 
perfect. The upper bone is the metapterygoid ( mt.pg .), it occupies the neck of 
the suspensorium, leaving cartilage, however, on the concave articular facet—for the 
basipterygoid—and also on the short round “trochanter,” below the joint; this spur 
is the arrested otic process (ot.p.)* 
The quadrate (q.) is a bony quadrant running, at its angle, close to the articular 
condyle ( q.c .) ; this latter is an elegant convexo-concave trochlea, with its largest 
convexity on the outside. The main part of the body of the suspensorium is 
unossified; it is a large oblong tract, with its postero-inferior angle rounded off; 
it is rather hollow outside and convex within, where it is invested by the pterygoid 
bone (pg.). 
The pterygo-palatine rod (p.pg.) is unaltered since the last stage; it never ossifies, 
and reaches as far forwards as the cornua trabeculae ( c.tr .), 
The articulo-Meckelian rod (mh, ar.) has increased in size (both actually and 
* In Plate 38, fig. 5, below, for pa. read pd. 
