56 OSBORN. [VoL. II. 
(Osborn, ’86, Fig. 2, text), which I have suggested may be 
remnants of the embryonic neuromeres. The origin of the 
cranial nerves is described elsewhere. 
The Ventricles of the Brain. A comparison of the encephalic 
ventricles of these genera, in longitudinal section, brings out 
some interesting facts, Figs. 7, 8,9. Cryptobranchus approaches 
the piscine type, and Rava the Sauropidan type: they are at 
opposite ends of a series. The roof of the C7yptobranchus brain 
is nearly straight in the mid-region ; in Rana it is much folded, 
so that the cerebellum and postcommissura are brought to- 
gether; these folds and the lateral outgrowth of the optic lobes 
produce the diverticulum of the mesoccele, the optocoele 
(Wilder), and the tori-semiculares in the walls. The position of 
the trigeminal nucleus affords a means of comparing the optic 
lobes of the Uvodela and Anura (see below). A still more im- 
portant difference is in the fore-brain. In Raza the cerebral com- 
missures lie in the lamina terminalis proper; there is no extended 
ventriculus communis. In the lower Uvodela (the Sala- 
mandridé have not been examined), the commissures trav- 
erse a fold ‘of the dloonr and “there 1s a largevvem 
triculus communis in ’front-of this, 2, Fie. 7 Was 
vus shows a remarkable development of the ventricular plexuses, 
which extend well into the lateral ventricles and backwards 
nearly to the cerebellum. The elevation of the floor which con- 
tains the corpus callosum and anterior commissure is very 
similar in position to the commissural band between the cor- 
pora striata in the Teleosts. (See Appendix, Note 7.) 
SEGMENTATION OF THE BRAIN. 
Under this head we may consider the larger encephalic seg- 
ments and pass by the neuromeres, which, as recently de- 
monstrated by Orr ('87, p. 335), have a special significance with 
relation to the origin of the cranial nerves, exclusive of the first 
and second pairs. The neuromeres and central nuclei, when 
fully investigated, will undoubtedly enable us to establish a 
closer comparison between the brain and spinal cord segments 
than can ever be drawn from the peripheral distribution of the 
cranial nerves. 
As above pointed out, the chief points of contrast between 
the brains of the Azuwra and Urodela are the large optic lobes 
