RATHKE ON THE DEVELOPMENT OE THE CRANIUM. 249 
markable ring which Cuvier has termed the ‘ os en ceinture.’ But 
whether this part corresponds with a part of the ethmoid of the 
higher animals, as has been generally admitted since Cuvier’s time, 
or whether it does not rather correspond with the orbito-sphenoids 
of the higher animals, can be satisfactorily answered only by the 
study of the development of the urodele Batrachia. The analogy with 
the orbito-sphenoids, structures which otherwise would be absent, is 
favoured by the enormous size of the bones in Bana ocellata, as also 
by the circumstance that in many osseous fishes, e. g. the Cyprinidae, 
the ali-sphenoids, related bones, coalesce by their lower ends with 
one another, and not, in the regular way, with the body of the 
sphenoid. 
§ 15. Recently, I have observed, in embryos of Blennius viviparus, 
whose yelk sac had only a moderate volume, that the notochord, as 
in other vertebrata, extended only to between the auditory organs, 
and that the part of it situated in the head, was produced anteriorly 
into a point, so that, in relation to its base, it had the form of a toler¬ 
ably elongated cone. Yet the cavity of the cone, wide at its posterior 
extremity and filled by the nucleus of the notochord, did not extend 
to its anterior end, but only to its anterior fourth. The part sur¬ 
rounding the cavity, however, consisted of the primitively very thin 
membranous sheath of the notochord and of a somewhat thicker 
sheath, also forming a hollow cone, of bone, which was continued 
right and left into a narrow and very thin ala. 
Anteriorly and laterally this wholly bony part, which constituted 
the basi-occipital, was inclosed by a tolerably broad but only very 
thin stripe of cartilage which formed a fringe round it. Hence, the 
posterior part of the basis cranii was in part already ossified, while, in 
part, it had remained cartilaginous. Anteriorly, the cartilaginous part 
extended in the middle line of the head as far as the pituitary body : 
right and left, however, it was continued much further forwards, and 
the trabeculae had the form of two thin and moderately broad bands, 
which ran tolerably parallel with one another, and the opposed edges 
of which were sharply defined; the interposed gap was filled with a very 
delicate layer of cellular tissue, presenting no such cartilage corpuscles 
as those which occurred in the bands themselves. Just in front of the 
pituitary body, the trabeculae united again and passed into an azygos, 
somewhat narrower but much longer and thicker cartilaginous pro¬ 
cess, which extended to the anterior end of the head, and here came 
into contact with the maxillary and premaxillary bones. 
Its breadth remained pretty much the same throughout, for only 
quite in front did it become somewhat broader: and here, on each side, 
there could be remarked a small outwardly directed prolongation, these 
prolongations indicating the two cornua into which the coalesced part 
of the trabeculae is produced anteriorly in other animals. On its under 
side, however, the cartilaginous process, or the coalesced part of the 
cranial trabeculae, possessed a narrow and moderately deep groove, 
which traversed it from its posterior almost to its anterior end. Bur- 
