898 PROFESSOR W. C. M‘INTOSH AND MR E. E PRINCE ON 
There is thus much less complexity in the stages just described than shown by Batrour 
and ParKER in the notochord of the Ganoids.* 
Skull.—Much has been done in regard to the development of the cranium of 
Teleosteans, and the comparatively recent memoir of Mr Parxert specially treats of the 
skull of the salmon, so that it will be necessary to give only a brief account in these pages. 
On escaping from the ovum in January, the cranium of the wolf-fish is im a very 
rudimentary condition. The greater part of the vault is covered by a thin layer—the 
external cellular integument with a membranous layer beneath, the former showing a 
considerable thickening above the prominent ocular region similar to the tissue—con- 
sisting of pulpy columnar cells—in Gadoid larve 4; inch long. In vertical section 
the first skeletal elements in this region are the anterior ends of the trabecule (PI. 
XXIII. fig. 1, and Pl. XXIV. figs. 5 and 6, t), which seem to have united in front, as in 
the salmon of the first day, and form a kind of ridge, with a superior convexity. They 
extend downward and inward, leaving a space behind the pituitary body, and appear 
to merge in the parachordals which lie on each side of the notochord. The notochord at 
its commencement abuts, in fact, on the cartilaginous plates just mentioned. The inner 
ends slightly curve upward, and do not appear to touch. The parachordals in the 
post-larval Pleuronectid, 5%; of an inch long, furnish a great contrast to this condition, for 
their inner edges have coalesced, and form a dense plate of cartilage—into a cylindrical 
cavity in which the anterior end of the notochord passes. From this dense central plate 
thus pierced by the oral end of the chorda, two thin plates pass and unite with the 
otocystic cartilage on each side. The basilar plate now forms a complete floor in the 
posterior cranial region. Even more marked is the united condition of the parachordals 
in the young Clupeoid, % inch long, at the point where the notochord passes into the 
cranium—the coalesced part having, in transverse section, the form of a massive oblong 
element penetrated centrally by the notochord. Posteriorly, as the diameter of the 
notochord increases, the cartilaginous investing mass diminishes, until between the ears 
it is represented merely by four angular nodules of cartilage, two at the upper and. 
two at the under side of the chorda. In the post-larval goby, 3°; inch long, the 
parachordals unite, but they form a comparatively thin, flattened, basilar plate, into which 
the chorda passes, and their lateral extensions unite with the otocysts and continue 
upwards over the hind brain—the posterior part of the chondro-cranium being, in fact, 
now wholly cartilaginous, and this complete tube of thin cartilage continues into the 
occipital region, and encloses the medulla oblongata. The small Gadoids, 4°; inch long, 
show a similar condition of the posterior floor of the skull, the thin cartilaginous 
parachordals uniting with the floor of the otocyst on each side; but the roof is still 
membranous above the fourth ventricle. There is a remarkable development of black 
pigment in the lining membrane of the otocystic cartilages—the corpuscles being situated 
* The development of the vetebral elements of Teleosteans at St Andrews has been undertaken by Prof. D. J. 
CunninGHaAM, of Dublin. 
+ Phil. Trans., vol. elxtii., 1873, pp. 112-145, plates i.-v. 
