414 
MR. W. K. PARKER OX THE SKELETON 
The side walls of the chondrocranium of the Lamprey are well developed (Plate 18. 
figs. 1—5), but, as in Tadpoles, and adult Anura also, the optic and trigeminal nerves 
(II., V.), pass out of considerable fenestrce, and not out of mere foramina. The 
orbito-sphenoidal region (fig. 5, o.s .) is wider than the alisphenoidal ( cd.s .), but the 
latter mounts up into the roof, and the two sides meet round the middle, and fore 
part of hind, brain (Plate 18, figs. 3, 5, t.cr.) The occipital ring does not exist, and 
the hard part of the basi-occipital, as we have seen, is abortively developed. 
In front of the posterior sphenoidal “tegmen” there is a large pyriform fontanelle, 
the broad fore part of which is largely covered by the hinder part of the double , 
mammilliform nasal capsule— -(na.) an independent structure, as in the Tadpole, larval 
Urodele, and Elasmobranch ; this is composed of soft cartilage. 
The facial outgrowths of the Lamprey’s skull are confusing, because of their 
extreme simplicity, and because of the absence in them of the normal segmentation 
from the basis cranii. Yet the Lamprey is not alone in this peculiar and generalised 
state of the cranio-facial cartilage; it occurs in so many other Ichthyopsida, especially 
in the more archaic types, that I am strongly induced to look upon it as the retention 
of an ancient condition of the skull of the Craniata. 
Except in the basal (ventral) region, there is no segmentation, and there the parts 
are so unlike those of other Fishes that some of these basi'-visceral cartilages are of 
doubtful morphology; the question being whether they belong to the deep or super¬ 
ficial category. 
Of parts formed inside the “ head-cavities ” there are only representative regions of 
the 1st and 2nd post-oral arches, and it is evident that the 1st or maxillo-man- 
dibular is abortively developed below, and the hyoid abortively developed above; 
the basal part of the latter, as well as its sides, are clear, but the mandibular region 
is very doubtfully represented at all. 
The only tract that can be said to belong to the proper branchial region (of “intra- 
branchials ”) is the hind part of the great lingual cartilage, behind the setting on of 
the lateral “ cornua” of the hyoid arch. 
In coming to details, I shall have to refer freelv to other work of mine, in other 
Ichthyopsida, and also to the views written, or expressed to me in discussion, by my 
esteemed fellow-workers; from one ofi the chief of these I can get no more counsel or 
help* 
* I have not felt myself able to stir a step without the help of Professor Huxley’s admirable paper 
already referred to, on the nature of the “Cranio-facial Apparatus of Petromyzon ” (Jour, of Anat. and 
Phys., vol. 10, plates 17, 18, pp. 412-429). I say this the more freely because I feel satisfied that the 
author of that paper will give me credit for having thrown some useful additional light upon the subject, 
thus necessitating a considerable divergence of opinion between us as to the meaning of some of the parts. 
The manner in which the late Professor Balfour always demanded incontrovertible proof of any view I 
might be holding at the time of discussion has served to make me work with extreme caution. With regard 
to one difficulty mentioned by Professor Huxley in the paper just referred to (p. 423), as to the distri¬ 
bution of the branches of the 5th nerve, I may mention that in two or three years after its publication 
