Vertehroid Homologies of the Cranium in Vertebralia. 63 
" The dorsal laminse first coalesce in the middle cephalic 
region, extending forwards and backwards. The ceiDhalic 
canal is separated into three distinct dilatations or cerebral 
vesicles, of which the anterior is the largest." Subsequent 
flexure of the vesicles divides the cavity of the cranium into 
pro-cranium and meso-cranium, at angles to each other; as 
development proceeds the meta-cranium and para-cranium 
cover the posterior lobes of the brain and cerebellum. The 
neur-arc forming the chondroid tunnel of the cerebrum and 
cerebellum, from the posterior occipital through the wormian 
and masto-parietal, coalesce with the ethno-frontal, and 
cover the ali-sphenoid and splieno-orbitaL The basi-cra- 
nium, composed of, (1.) basi-occipital ; (2.) basi-otic, or 
basilar ; (3.) basi-sphenoid, or basi-olivare ; from the rostrum 
sphenoidis the chondroid plate of the ethmoid and nasal is 
prolonged. This chondroid condition is well seen in the 
cranium of the Salmonidee, where the osseous frontal and 
parietal are easily forced off the cartilage, and the long 
basi-sphenoid is equally removable from the chondroid basi- 
cranium, which extends into the incisor or pre-mandibular 
palate, sometimes misnamed the vomer. Agassiz main- 
tained that the centro-chord did not extend beyond the 
sella turcica ; and Huxley seems to adopt the same opinion, 
though, strangely enough, he admits that in the Lancelot it 
extends to the utmost length of the animal, beyond the termi- 
nation of the myel-encephalon. It may be as well to re- 
mind the student that the relation of neuraxis and the 
hsemaxis t5 the digestive or intestinal tube is completely 
different in the articulate and vertebrate classes. In the 
segment of the crustacean and entomoid classes, the neur- 
axis is contained in a small canal below formed by the 
neur-arcs, but without any kaulon or central stem, and lies 
beneath the digestive or intestinal canal. The anterior or 
oral termination, passing through esophageal nervous ring, 
being the type of the par-encephalon behind with the audi- 
tory apparatus, while the mesencephalon and prosencephalon, 
with the optic and olfactory sense capsules, lie before. Thus 
the pharynx and mouth of the invertebral pass where the 
pituitary body and infundibulum (possibly the typical rem- 
