184 Proceedings of the Royal Physical Society. 
The ventral and lateral walls are not evenly thickened, but bulge into 
the cavity of the [Vth ventricle to form a series of more or less longitudinal 
ridges, three in number on each side. (i.) The Median Longitudinal Bundles 
(m.1.b.), forming the floor of the ventricle, are well marked and easily seen when 
the choroid plexus has been removed (Fig. 2). They are directly continuous 
with the tracts in the corresponding position in the spinal cord. The grey 
matter of the ventral horn, however, comes to lie in the outer grooves which 
separate these bundles from the next pair which lie dorso-lateral to them. 
These, (i1.) the Visceral Sensory Columns (v.s.c.), are not in themselves evenly 
thickened but present a row of swellings, easily seen when the brain is 
divided into two by a median sagittal section (Fig. 5). The number of the 
swellings is five, and they have been considered as the nuclei of part of the 
Xth, the whole of the 1Xth, and part of the VIIth Cranial nerves: according 
to Johnston the column is the terminus of all the fibres from the visceral. 
surfaces of the head. The last pair of ridges is that of (ii1.) the Somatic 
Sensory Columns (s.s.c.), which form the rest of the lateral walls of the ventricle. 
Anteriorly they become double by the superposition of the Lobi Liniz 
Lateralis, one on each side. ‘These lobes are so named because they are 
connected with the fibres of the Lateralis system found in the Vagus and 
Facial nerves. The posterior portions of these lobes, which are more 
conspicuous externally than in Scylliwm, are best seen in the half-brain. 
The anterior portions of the lateral walls project forward, on either side 
of the Cerebellum, as a pair of frilled appendages, the Restiform Bodies 
(Figs. 2 and 4,7.b.). The dorsal wall is thin, but the lateral ones are increased 
in area by a certain amount of foliation: the inner wall of each is in 
direct communication with that of the other by a thick transverse band 
which lies under the Cerebellum but arches over the cavity and forms the 
thickened anterior portion of the dorsal wall of the Medulla referred to 
above (Fig. 5). 
The Cerebellum is not particularly well developed; perhaps not quite so 
much as in Scyllium. Its dorsal surface is marked by two grooves : a median 
longitudinal sulcus, which, however, does not extend to the anterior end ; 
and a transverse one, a little in front of the middle. The walls are very 
thick so that the cavity is almost entirely obliterated. Johnston has figured 
the median sagittal section of the brain of Sgualus acanthias, which shows a 
Cerebellum much more complicated, although, as the specimen should be of 
the same species as A. vulgaris, the figures should agree. 
This completes the description of the Rhombencephalon, except for the 
nerves which emerge from it. Some of these differ markedly from those of 
Scylliwm. | 
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