196 PROF. W. K. PARKER ON THE STRUCTURE AND 
part are parachordal, and that their prochordal part is, as Rathke long ago asserted 
with regard to the Snake, a production forward of their parachordal or main part. 
The large cranial part of the notochord is embedded, like a Belemnite, in the basis 
cranii; and on its sides, in the cranial region, there are two muscle-plates (my); the 
third pair of plates in the figure (my) are spinal. 
The hinder part of the cranial notochord (nc) has no investing cartilage, right and 
left; and all the rest of the cartilage, at present, belongs to the sense-capsules and 
the visceral arches. 
The crested trabecule (7), at present, scarcely reach to the anteorbital region, and are 
only slightly curved inwards in front ; for four fifths of their length they are prochordal ; 
and at present they are rounded rods. The auditory capsules (aw) are subglobular, 
and are already coated with a thin layer of cartilage; these da//s are at a considerable 
distance from the hind part of the trabecule; and the mass of cells forming the 
Gasserian and geniculate ganglia (Vv, vil) intervenes right and left. 
In front of the capsule the suspensorium runs outwards from the middle of the 
trabecular curve, to which it is becoming fused; there is no division of the pedicle 
(pd) at present; but the otic process (of.p) has already budded out, and is applying 
itself to the antero-external edge of the capsule. 
The direction of the body of the suspensorium is outward and forward; and the 
condyle (q¢. ¢) is opposite the middle of the mid brain (c’). 
The mandibles (mh) are one third longer than the suspensoria; their articular part 
is rounded, and their distal end is narrow and almost pointed; the dentary (d) and 
splenial (sp/) are already apparent; and the teeth on the latter are relatively large. 
In front of the nasal capsules (0/) there is a transverse spicula of irregular bone 
carrying two teeth, this is the preemaxilla (pz). 
Under the fore palate, within and behind the nasal sacs, there is on each side a 
spindle-shaped tract of irregular bone carrying a rasp of teeth. This tract is sub- 
dividing into two subequal pieces: the foremost is the rudiment of the vomer (v); the 
hinder tract is the palatine (pa). 
In the figure the upper aspect of the head is shown, and the hind brain has been re- 
moved from over the notochord and muscle-plates; the pituitary body (py) is seen at the 
apex of the notochord; the eyeballs and earballs are of about the same size. 
Behind the latter a mass of cells is seen; these are the rudiments of the ganglia of 
the ninth and tenth nerves (IX, X). 
Under the skull-floor a membranous film was becoming bony; this was the 
beginning of the parasphenoid. After this, very soon, bony tracts appear above 
the brain-cavity and outside the ear-capsules; these will be the frontals, parietals, 
and squamosals. The maxillaries are later in their appearance; and the very sub- 
stance in which the endocranial bones form is not developed more than in rudiment. 
J have not figured the postmandibular arches ; they were becoming cartilaginous. 
