954 
MR. A. SANDERS ON THE ANATOMY OE THE 
that the suggestion thrown out by me in 1878 , that the oesophagus of the primitive 
ancestors of the Vertebrata passed through the infundibulum, should also have occurred 
to Professor Owen, who, in a paper recently read before the Linnean Society, entitled 
“ Homology of the Conario-Hypophyseal Tract, or the so-called Pineal and Pituitary 
Glands,” showed that in the embryo there are indications of there having been a 
communication between the primitive intestine (before the permanent mouth appeared) 
and the canal going through the infundibulum and the third ventricle to the present 
dorsal surface of the brain, so that the lateral walls of the third ventricle and the crura 
cerebri in Sharks and (consequently in Teleostei) homologise with the commissures 
between the supra and infra-oesophageal ganglia of insects. 
The second fixed point would be the ganglion of origin and the place of exit of the 
oculomotorius. If the foramen of exit of a cranial nerve be sufficient to fix the 
homology of the bone of the skull through which it passes, then it must be conceded 
that the ganglion of origin of a nerve ought to fix the homologies of the parts of the 
brain lying near it. 
We have then these two fixed points, and applying them to the central nervous 
system, we find that the first indicates the third ventricle or thalamencephalon, and 
consequently the posterior commissure, which two parts have always a fixed relation 
to each other. The determination of the posterior commissure incidentally involves 
that of the corpus quadrigeminum ; for Forel* shows that this commissure is in 
juxtaposition to the transverse commissure of the anterior corpus quadrigeminum ; so 
in Fishes the posterior commissure is in close relation to another commissure which 
Fritsch marks c. anterior, but which is nothing more than the continuation forward of 
the transverse commissure of the tecta lobi optici. This line of argument is supported 
by the consideration of the position of the ganglion of the oculomotorius, which in the 
Mammalia is placed immediately beneath the aqueduct of Sylvius and the anterior 
corpus quadrigeminum. In Fishes the corresponding ganglion is placed beneath the 
ventricle of the optic lobe and the tectum lobi optici. 
In one of his figures! Fritsch has made it appear as if this ganglion were at the 
side of the aqueduct of Sylvius instead of beneath it, as it ought to be. 
This converging line of argument is supported by another mode of reasoning based 
upon structure, which although taking a subordinate position is yet of use, as supporting 
considerations derived from other sources. Thus MeynertJ has shown that in the 
human subject the anterior corpus quadrigeminum contains radial fibres on which 
fusiform cells are developed. The tecta lobi optici in Fishes have radial fibres with 
fusiform cells developed thereon. 
The united force of these arguments compels me to homologise the tecta lobi optici 
* Beitrage z. Kentniss des Thalamus Opticus, &c. Sitzber, d. k. Akad. der Wiss., Wien, Bd. lxiii. 
Math. Nat. Olasse, fig, 4 ; also Meynert, fig. 249, l.c. 
f Loc. tit., fig. 32. 
'! Log. tit. 
