306 = Prof. Owen on the Answerable Divisions of the 
brains of the lower Vertebrates. It needs only to refer to the 
comparative anatomy of the brains of fishes; and here I would 
refer to a late contribution thereto by the accomplished 
“ Docent der Anatomie zu Berlin,” the ‘ Oberstabsarzt Dr. 
Rabi-Ruckard,” entitled ‘‘ Das Grosshirn der Knochenfische 
und seine Anhangsgebilde.” A reference to the figures 1 and 
2 of Taf. xii. of this memoir in the ‘ Archiv fiir Anatomie 
und Physiologie,’ 1883, of a trout’s brain (Salmo farto) suffices 
to show the homologous space under the name of “ ventriculus 
tertius.”” It is one of the demonstrations of the foregoing homo- 
logy. The amount of neurine in the lateral] walls of this 
interspace due to the continuation of cerebral tracts homologous 
with those uniting the prot- and epencephalic divisions of the 
Cephalopodal brain, commonly termed “ supra-” and “ infra- 
cesophageal ’”’ ganglions, is somewhat greater in the fish, and 
the alimentary tract which in the Cephalopod traverses that 
interval, is represented in the Vertebrate by the modified 
remnant of the primitive gullet. This remnant extends 
upward (dorsad) beyond the fish’s brain, penetrates the carti- 
laginous basis of the frontal bone, and is there arrested; in 
the opposite or “ ventral ”’ direction the “ transcerebral tract” 
extends into the cartilaginous basis or floor of the cranium, 
which shuts off its original communication with the pharynx ; 
the so-obstructed or closed parts of the transcerebral tract are 
converted into the parts called respectively the “ pineal” and 
“pituitary glands,” with the intervening “ ventricle” and its 
“infundibular” prolongation. 
Influenced by the foregoing facts, and reasonings there- 
upon, I deem the grounds for restricting the homologies of 
the nerve-centres of Vertebrates and Invertebrates to one 
portion only of the brain of the latter, known as the “ supra- 
cesophageal ganglion,” to be inadequate; and a sense of this 
inadequacy led me to institute the series of embryological and 
other researches on the conditions of the course of the gullet 
through the brain-centres of Invertebrates which were sub- 
mitted to the Biological Section of the British Association 
at the Meeting held at York in 1881*,. This communica- 
tion was followed by the “ Researches on the Homologies 
of the Neural Centres, their Parts and connected Nerves,” 
submitted to the Linnean Society of London in 18827. 
The conclusions to which I was led enabled me, or seemed 
to me, to show that the position in which the body of an 
animal is carried in relation to the earth’s surface is of less 
* “Reports,” &c. in ‘ Transactions of the British Association,’ &e. for 
1881. 8vo. 
+ ‘ Journal of the Linnean Society, Zoology, vol. xvii. 1882. 
Li 
