OF THE MARSIPOBRAHCH FISHES. 
441 
width. At this part they embrace the lower part of the front of the membrano- 
cranium, in front of the pituitary space. 
The basal bars in their pro-chordal region (tr.) are thickest in their middle, but do 
not lessen much in front, they are, in form, like a pair of callipers, and end in a 
blunt point which is turned a little towards its fellow. The bars are tilted upwards 
and outwards (Plate 24, figs. 1-4, tr. ; and Plate 25, fig. 2, iv.). 
A little in front of the auditory capsules we see on each side a small blunt hook of 
cartilage, turned forwards at its free end, but growing directly outwards from the 
trabeculse without any sign of segmentation ; these are the primordial rudiments of 
the pedicle and pterygoid ( pd., pg.). These first, continuous rudiments of the face are 
of great interest, as we shall see by comparing them with their counterparts in other 
Tchthyopsida. 
So also is the condition of the primary basi-cranial bars or trabeculae, which on their 
hinder part embrace the notochord as parachordals (or investing mass), but from the first 
are rather related to the fore brain as its proper supporting skeleton, than to any 
other part. Their union in front of the trabeculae, and their continuation forwards, as 
cornua, are secondary matters, and vary very much in different types, but their most 
important character is their continuity, for they show no signs of being under the 
influence of any segmentation that may be developing in the head. Here, the basal 
bands are longer, but much narrower, in their parachordal than in their prochordal 
regions, but in the nearest relations of these Petromyzoids, the “ Anura,” they only 
embrace the apex of the notochord by their hinder end, and form their cornua before 
they unite at the mid-line. In those Amphibia the parachordal region is developed 
as a backward extension of the trabeculse, but in the Urodela that part is developed 
independently, and the cornua trabeculse may appear first as ongroivths of the trabeculse, 
or afterwards as outgrowths. Then, as to the facial part of the skull, or upper jaw, 
(the upper part of the 1st branchial or visceral arch), which is greatly developed forwards 
over the mouth in all known Yertebrata, we see that in the Lamprey the pedicle with 
its hooked end or rudiment of the pterygoid cartilage is developed from the first as 
an outgrowth of the trabecula, and the rest of the arcade—its palatine portion growing 
on to the ethmoidal end of the trabecula—does not appear until after transformation. 
In the Anura the whole arcade is primary, and is primarily one with the trabeculse, 
both the pedicle and the ethmo-palatine tract being continuous with the basal bar. 
In the Urodela nothing of the sort exists; the pedicle and its ascending process 
are developed as the bifid free top of the suspensorium ; afterwards both unite with 
1 the skull in some kinds ; in others only the ascending process. In them the palatine 
with its ethmo-palatine process, is an early free cartilage ; the pterygoid process of the 
suspensorium is a late outgrowth, and only in one kind known ( Rcinodon sibiricus *) 
does the subocular arcade become continuous. On the other hand in the genus Bufo, 
* See WiEDEBSHEiM, ‘Kopfskelet der Urodelen,’ 1877, plate 5, fig, 69. 
