398 
MR. W. K. PARKER OK THE STRUCTURE AND DEVELOPMENT 
(figs. 4, 5, G, 9, c.tr.), and below tlie tissue which becomes the single pre-maxillary 
(fig. 5, px.). 
From this, the bowed outer edge contains a pith which becomes the maxillary, and 
the inner, in like manner, the rudiment of the palatine bones, whose ascending process 
is prefigured by the lobes that constrict the inner nasal passage ( i.n .). 
The outer and inner bands are united obliquely behind by a tract which becomes the 
transpalatine, and the hind part of the inner band developes the pterygoid. 
The two folds in front of the inner nostril contain the tissue that becomes the right 
and left vomers ; the circular marking behind the opening, is the pituitary body (py.). 
The mandible (figs. 2 and 7, q., mk.) is now composed of two cartilages : a suspensory 
piece or quadrate, and the articulo-Meckelian rod. 
The former has an anterior blunt process above, the stunted pedicle ; and a longer 
otic process (fig. 7,p>d., ot.p>7). 
As in the Salmon, the segmentation of the rod is such as to make a hinge between 
the two parts with a long angular process to the lower segment. 
This lower piece ( ar . mk.) is a long sigmoid rod, thickest above, and then uniformly 
terete ; the axes of the two segments are coincident, and their direction downwards 
and forwards forms a very acute angle with the basis-cranii. 
The hyoid fold (hoy. ) has cartilage only in its upper third ; this is a rib-like piece 
with a rounded capitulum, a solid tuberculum, and a sickle-shaped shaft, whose 
convexity is backwards. 
The hind edge below has a crest ready to separate from the main part. 
The capitulum is attached to the membrane of the fenestra ovalis (st.), which is 
beginning to chondrify continuously with the hyoid rib-like rod ; the meaning of 
these parts will be seen in the next stage. 
Fourth Stage. Embryo Snakes, 2-§ to 3 inches long. 
In the last stage the chondrocranium was perfect, and granular tracts along the 
palate and face were beginning to ossify. 
Yet only the hind part of the hind brain was covered with cartilage, and the fore 
part of the cranial floor had merely two rounded threads of cartilage supporting it ; all 
the rest was membrane. 
About five-sixths of the Snake’s skull is made up of subcutaneous, supplementary 
bones ; is dermo-skeletal, in fact. 
This stage shows the origin of most of the endoskeletal centres of the limited 
chondrocranium, and nearly every centre whose origin is in a mere membranous tract. 
The shape of the chondrocranium was. perfect in the last stage, so that the main 
work to be done now is to show its histological transformation. 
The first bony part to be noticed is the ceplialostyle or bony sheath of the cranial 
notochord. It is perfect now, and has begun to infect the cartilage right and left, so 
as to widen the tract that becomes the broad basi-occipital (Plate 29, fig. 5, bo.). 
