558 
MR. W. K. PARKER ON THE STRUCTURE AND DEVELOPMENT 
coping to the soft hinder half of the skull-wall (fig. 3, 'pro.) ; it alters but little of the 
soft Avail beneath it, and ends as a spike near the bony ethmo-sphenoidal tract ( e.sp .). 
Beneath (fig. 4) there is no such strength added to the foundation of the wall, although 
the floor, like the roof, has an extraneous source of strength, in the latter derived from 
the parietals and frontals, and in the former from the parasphenoid (figs. 1 & 2, pa.s., 
f, p .). The stapes ( st .) will be described with the suspensorium. The ethmo-sphenoid 
bones ( sp.e .) are manifestly the lateral rudiments of the Batrachian girdle-bone, without 
the upper azygous piece (the superethmoid), and left unfinished in their growth. The 
part formed by the original fore ends of the trabeculse is here very solid, and is well 
covered with bone-deposit, which ends abruptly both before and behind, above; 
but in front on the lower face the bones form sharp wedges, piercing the huge flat 
underface of the internasal plate (fig. 4). Below, also, they are their own width apart ; 
above, they meet in front of the lower fontanelle and the fore brain, and the olfactory 
crura rest upon these conjugating processes (1, fig. 3). 
At the margin of the upper fontanelle these bones are wide apart ; and here the 
cartilage rises into a crescentic mound, whose concave edge looks backwards on each 
side ; and, in front, the cartilage is bevelled. 
In front, the internasal tract ends so as to form a semielliptical notch between the 
large, flat, trabecular horns ( i.n.c ., c.tr.) ; on these the reniform nasal capsules are 
mounted, and with them they are coalesced. The united crura are largest where they 
have attached to them the small antorbital cartilages («.o.), and the underface of this 
ethmonasal tract is large, flat, and roughly pentagonal ; for below, the “ horns,” 
where they become free, are bevelled (fig. 4) ; they diverge gently, and end in front with 
a sinuous margin. Above (fig. 3), the naso-trabecular building is very elegant ; for these 
most simple nasal roof-cartilages (first “ paraneurals ”) rest in front on the middle of the 
cornua, and behind overlap the ethmoidal region ; the outer nostril ( e.n .) is finished 
behind by a fibrous valve, and not by a cartilaginous labial, as in the Frog. 
The inner nostril ( i.n .) is much further outwards, being external to both the vomer 
and the dentigerous osseo palatine. 
The suspensorium of the mandible is a part of the chondrocranium, and a very large 
part too, and may be fitly described here. 
The quadrato-pterygoid cartilage is now a morphological counterpart of that of the 
Selachians, with this great difference, namely, that it has three processes attaching it 
to the cranium that are mostly represented by membrane in them. 
These processes, the pedicle and the ascending and otic processes, are, two of them, 
attached by a strong fibrous web to the basisphenoidal and auditory regions ; the ascend- 
ing process keeps its confluence with the side wall of the skull. That process (figs. 3, 5, 
a.p .) is a thick rod, and it is separated by a shallow groove from the shorter but still 
stouter pedicle (pd .) ; through the angle of the fork run the Vidian and orbito-nasal 
nerves. The postero-external or otic process ( ot.p .), as also the main part of the sus- 
pensorium, is convex above and hollowed out below. A large bony spatula now runs 
