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 trabeculae {tr), 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 {au) are subglobular, 

 and are already coated with a thin layer of cartilage ; these halls are at a considerable 

 distance from the hind part of the trabeculse ; and the mass of cells forming the 

 Gasserian and geniculate ganglia (v, vii) 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 {ot.'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. c) is opposite the middle of the mid brain (c^). 



The mandibles {mk) 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 {spl) are already apparent ; and the teeth on the latter are relatively large. 



In front of the nasal capsules {ol) there is a transverse spicula of irregular bone 

 carrying two teeth, this is the prsemaxilla {px). 



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 appeai'ance; and the very sub- 

 stance in which the endocranial bones form is not developed more than in rudiment. 



I have not figured the postmandibular arches ; they were becoming cartilaginous. 



