DEVELOPMENT OF THE SKULL IN THE LACERTILIA. 
621 
yet developed, owing to the immature state of the trabeculae cranii, on whose “ horns,” 
or outgrowths, this twin facial fold is formed. 
Beneath the hemispheres, on each side, inside the nasal fold, there is a second mass 
of cells, deeply pitted; this is the nasal gland, the pit is its “ lumen ” or future duct, 
and the tissue over and under it will be the vomer and septo-maxillary. 
The massive palatine fold is separated by a notch from the outer nasal fold (rax.p., ol.) 
and this part shelves inwards towards the base of the still membranous cranium; the 
thin, inner part will contain the palatine bone. The broad, concave floor of the skull 
is suddenly, for a large circular space, deficient, below the junction of the fore and 
mid brain. 
Above this part (Plate 37, fig. 3, C l ) the “ thalamencephalon ” merely shows a rudi¬ 
ment of the tube, which in the adult is called the “ infundibulum,” but the fore brain 
here at its postero-inferior part, is quite closed. 
Under this part, where the floor is wide open, the oral fold has developed an 
inverted cup, with its fundus towards the brain, and its narrowing mouth looking 
downwards and a little backwards. 
This is the rudiment of the “ pituitary body ” (Plate 37, figs. 3, 7, and Plate 38, fig. 1, 
pyf which, contrary to what is seen afterwards, is closed above and wide open 
below; the sides of the pituitary space are lipped to embrace this unaccountable piece 
of morphology—a sort of empty pocket made of the epiblast of the mouth. 
Over this pocket, the axis of the embryo runs up half way to the frontal wall at right 
angles to the fore part of the head ; this mass of tissue is the “ middle trabecula ” of 
Rathke : a transient structure, as he pointed out. Along the back of this (Plate 37, 
fig. 3, m.tr., nc.) a less transient part of the embryo runs ; this is the notochord; it 
reaches almost to the top, becoming sinuous as it grows less and less. 
On each side of the notochord, lower down, there is a mass of granular tissue ready 
to become cartilage, and on each side of the pituitary space, up to the nasal region, a 
smaller curved bar runs; the latter is the trabecula, the former the “parachordal” 
band. 
Neither the true half section (Plate 37, fig. 3), nor the section which contains a 
third of the head (fig. 5), show these bands ; the one is outside and the other inside 
of these symmetrical basi-cranial rudiments. I shall show their structure in the next 
stage. (See Plate 37, fig. 8.) 
By slicing off a third of the head, vertically, I get what is shown in Plate 37, figs. 
4 and 5 ; fig. 4 is shown from the outside as a transparent object, and fig. 5 from the 
inside as an opaque object. 
Here Mr. Balfour’s researches on the ‘ Elasmobranchs ’ are repeated and verified, 
as indeed they are on the pituitary body. 
These figures show part of the pericardium and heart fed,., h.), the enclosing 
* The true organic punctum terminate is close in front of the part from which the infundibulum grows 
out. 
