CENTRAL NERVOUS SYSTEM IN VERTEBRATE ANIMALS. 
761 
vagi represent a mixed system of anterior and posterior roots, which correspond partly 
to the anterior and partly to the posterior roots of spinal nerves: thus confirming a 
conclusion previously arrived at by Gegenbaur. 
Spinal nerves (figs. 6 and 7).—The ventral roots of these nerves emerge as a bundle 
on each side of the raphe, from the internal inferior surface of the ventral horn of 
grey substance, and, taking a direction nearly downwards, pass out to form the 
ventral roots of the spinal nerves. 
The dorsal roots enter the cord obliquely, and there divide into two cords : one cord 
from the anterior part of the root passes backward, the other cord from the posterior 
part of the root passes forward ; they cross over the next nerve both in front and 
behind, and join the lateral columns of the cord. 
I am unable to do more than confirm the account which Sited A'" (who was the first 
to describe this arrangement) gave. 
Conclusion. 
A comparison of the brain of the Plagiostomata with that of the Teleostei brings 
out several differences in detail ; but the general scheme is the same in both. 
In the Plao’iostamata the lobi olfactorii have a well marked ventricle, communicating’ 
by a passage through the peduncle with a ventricle in the cerebrum, which anteriorly 
is double, but behind is single. There can be no doubt that these correspond to the 
lateral ventricles, while the posterior single part, which is continuous with the third 
ventricle, can be no other than the Foramen of Monro. The position of the anterior 
commissure, which connects the two sides of the ventral part or floor of these ven¬ 
tricles, would seem to indicate that the corpora striata should be looked for here. 
The Teleostei possess none of these structures, with the sole exception of the anterior 
commissure ; in them the olfactory lobe and the cerebrum are solid. 
The theory of Rabl-Ruckhard t is scarcely applicable to the Plagiostomata. His 
conclusions are that the cerebrum in Teleostei is homologous to the island of Reil and 
the corpus striatum only; while a layer of endothelium which lines the pia mater and 
forms a shut sac, communicating with the third ventricle, is genetically homologous 
with the unthickened wall of the cerebral hemispheres, “ Grosshirnblaschen,” and 
the space it encloses is the “ventriculus communis.” Other writers have compared 
the hemispheres in the Teleostei with the corpora striata, e.g., Tiedemann,| but of 
course this does not detract from the merit of this writer, whose reasoning and detailed 
exposition of the homology of these structures are worthy of attention. It remains 
only to be considered how far a layer of endothelium may be taken to represent 
* ‘ Zeitschr. Wissensch. Zoo!.,’ vol. 23, 1873. 
t “ Das Grosshirn der Knochenfische u. seine Anhangsgebilde.” ‘ Archiv Anat. Physiol.’ (Anat. 
Abth)., 1883, p. 307. 
f “ Anatomie und B i I dun gsgeschichte des Gebirns ina Foetus des Menschen.” 1816. 
MDCCCLXXXVI. 5 E 
