734 
MR. A. SANDERS ON THE ANATOMY OF THE 
The next writer, Viault,* turned his attention principally to the microscopic 
features of the brain of these animals ; he was almost the first to do so exclusively to 
the Plagiostomata. In a general way he was preceded by Stieda + in the Teleostei, 
but the investigations of this writer in the Plagiostomata were confined to the spinal 
cord only. 
Leydig | had long previously conducted researches into the microscopic anatomy of 
the Plagiostomata, but they were principally restricted to other organs of the body 
and were very slightly turned to the brain, in which, however, he succeeded in making 
a noteworthy discovery. 
Viault’s treatise, although very voluminous, contains no new facts, and the 
illustrations leave much to be desired, being stiff and apparently semi-diagrammatic. 
He did not neglect homology, and refuted Mikltjcho-Maclay on one side and 
Pohon and Fritsch, in advance, on the other; against the former he asserted the 
claim of the cerebellum to that name, and also showed how the optic lobes could not 
be the cerebrum, but were homologous with the corpora bigemina (“ tubercules 
jumeaux ”), and therefore belonged to the mesencephalon. The hypoarium he 
identified with the tuber cinereum. 
This writer, then, has adopted the ordinary interpretation of the various segments 
of the brain in these animals ; far otherwise is it with 11 oh ox. § It seems as if the 
more recent German anatomists were unable to put pen to paper without trying to 
suggest some new and more or less untenable views. With regard to the cerebrum 
and the cerebellum he agrees with the majority of the older writers, but in the battle¬ 
ground of homology—the optic lobes—he publishes some new views. He considers 
these lobes not as the mesencephalon alone but as a combination of the mesencephalon 
with the thalamencephalon; he remarks that this segment of the brain considered 
histologically consists of two completely differentiated masses, although macroscopi- 
cally they appear intimately united. The first mass, “ Zwischenhirn,” according to 
him, consists of a dorsal part which begins over the posterior part of the “ regio 
ventriculi tertii, and lies as a cover upon the “ Mittelhirn,” and, further, of a ventral 
part, which is formed from the infundibulum and lobi infundibuli and their ventricles. 
Between and behind these two masses the Mittelhirn is inserted. This consists of the 
roof of the aqueduct of Sylvius (on which the dorsal part of the “ Zwischenhirn” is 
applied), the floor of the same, and the nervous substance beneath. 
These authors complete the list of those whom I have been able to discover whose 
work has been confined to the elucidation of the central nervous system of the 
Plagiostomata. 
* “ Recherches histologiques sur la structure des centres nerveux des Plagiostomes.” ; Archives 
Zool. Exper.,’ vol. 5, 1876. 
f “Ueber den Ban des Riickenmarks der Rochen u. d. Haie.” ‘ Zeitschr. Wissensck. Zool.,’ rol. 23, 1873. 
J “ Beitrage zur Mic. Anat. n. Entwickelungsgesckickte d. Rochen u. Haie.” Leipzig, 1852. 
§ “ Das Centralorgan des Nervensystems der Selacliier.” ‘ Wien, Akad. Denkschn,’ vol. 38, 1878 
(Abthg. 2), p. 96. 
