442 
MR. W. K. PARKER ON THE SKELETON 
amongst the Anura, after being a mere wing or flying buttress of the skull daring 
the larval period, it becomes, in metamorphosis, broken up into separate parts, like 
that which is primary in the Urodela. 
In the Rays there is a pedicle, but it is a primarily independent cartilage, the fore¬ 
most of the “ pharyngo-branchial ” elements; in Sharks there is merely one, two, or three 
“ interbranchial rays ” in this part, and in all the normal “ Elasmobranchs ” the palatine 
region—which has a distinct segment in Rays but not in Sharks—is suspended to the 
skull by a ligament. In these types the trabecuhe are flat and wide, and chondrify 
first; afterwards, the parachordals become cartilaginous, but this condition runs on 
into the spinal region without any break, until the occipito-atlantal joint is formed. 
In Acipenser, a low type of Ganoid, the whole basi-cranial region is chondrified at 
about the same time, but in form is similar to what is seen in the Elasmobranchs. 
But the upper jaw is developed quite independently of the basis-cranii; its upper part, 
answering to the pedicle (or metapterygoid region), is a mosaic of cartilaginous pieces, 
with a median row, such as is seen in the ventral aspect, only, of the arches, in other 
types. 
Lepidosteus, a high Ganoid, comes nearer to the Suctorial Fishes and the Tadpole, for 
the palatine end of the upper jaw (palato-quadrate) is from the first continuous with 
the fore end of the trabecula, and so also is the pier (or pedicle ) of the hyoid arch. 
In that type I find no precedence of the prochordal tracts (trabeculae) in their 
chondrification; they, and the parachordal tracts, are one, and show no signs of 
distinction from the first. 
It is therefore evident that there is to be seen, in the early chondrocranium of the 
various Ichthyopsida, a mixture of the non-essential and the essential; these have to 
be winnowed apart by the Morphologist. I must return to this subject in my summary ; 
but it is manifest that the primary cranium exists merely as a pair of supporting bands 
from which, without segmentation, the facial skeleton may grow. The cartilages that 
arise in the intermuscular septa, in the spinal region, as rudiments of vertebrae, are a 
late product in the evolution of a Vertebrate; they possibly had no existence in 
countless types, the brain of wdrich had appeared in its three main vesicles, which, 
becoming larger and heavier, acquired pro- and para- chordal supporting balks. 
We saw (in Part I.) that one type of Fish, the Hag, more than a foot long, and as 
thick as a finger, with a highly complex cranio-facial apparatus, has no vertebral 
rudiments. This is true, also, of another (Bdellostoma), as thick as the wrist, and 
almost a yard long. 
This Myxinoicl condition remains throughout larval life in the Lampreys, and exists 
for a time, after the development of the basi-cranial bars, in the other Ichthyopsida. 
In the figure given of the embryo Lamprey’s skull (Plate 25, fig. 7 ; V., X.) I have 
shown the huge size of the ganglionic mass belonging to the 5th nerve (possibly that 
of the 7th included in this mass), and of the 10th or vagus. 
The auditory capsules ( au .) are evenly oval in form, and except where the 8th 
