PROSENCEPHALON OF SPINAX AS A TYPE OF ELASMOBRANCH FORE-BRAIN. 491 
fig. 4, in which one observes an aggregated central mass (e), namely, the paratermi- 
nal body (infra-foraminal precommissural body of Johnston), a lateral mass on each 
side of this adjacent to the medial wall of the ventricle (a), part of the corpus 
striatum. In fig. 56 of Johnston’s paper a transverse section of the brain of 
Acanthias is given, which represents practically the same condition as in my figure, 
but I draw different conclusions. The tuberculum olfactorium (6) (area superficialis 
basalis of Johnston) is clear in both. The paraterminal body (e) is also evident, and 
there projects towards the lateral ventricle a zone of cells (a), which Johnston terms 
the nucleus medialis septi. Gaupp’s description of this subpallial part may be 
summarised as follows. The subpallial part of the hemisphere can be distinguished 
into three regions — lateral, medial, and angular. The lateral part is the area of the 
basal ganglion of higher Yertebrata from which the basal fore-brain bundle takes its 
origin. The medial part of the hemisphere wall (“ the septum,” s. str.) can be differ- 
entiated into two areas of gray matter, namely, the central gray of the septum 
(Epistriatum R. R. y Cajal) ( e of my figure), and the area lying more in the concavity 
of the ventricular wall (a of my figure), which he terms the Ganglion mediale Septi 
(Ganglion primordial, Ganglion basal P. R. y Cajal). The pars angulare is situated 
round the ventral angle of the ventricle (fig. 4), and is to be regarded as a continuation 
of the gray masses which lie on the floor of the recessus superior of the thalam- 
encephalon. The pars angulare of Gatjpp is clear in my sections at the region pre- 
vious to the occurrence of the foramen interventriculare. It is, as Gaupp states, 
only obvious for a short distance. I regard it as part of the corpus striatum. The 
tuberculum olfactorium in the Amphibian brain does not appear to have the same 
definiteness as in that of the Selachian, but the facts seem to point to the proba- 
bility that the pars lateralis of Gaupp corresponds to part of the tuberculum 
olfactorium, likewise, however, to part of the corpus striatum. The central gray 
of the “septum” of Gaupp appears to correspond with the paraterminal body ( e of 
my fig. 4). A comparison of these areas of neurones with those given by Gaupp in 
the pars subpallialis is, however, a matter of some difficulty. 
The areas of neurones already noticed in the prosencephalon pass in the prse- 
thalamus and thalamencephalon into the arrangement shown in the text-figs. 1—3. 
Text-fig. 1 represents a diagram through the thalamencephalon. The tuberculum 
olfactorium, corpus striatum, corpus paraterminale, primordium hippocampi, and 
formatio pallialis are present in a modified condition. The formatio pallialis lies 
dorsal to the upper extremity of the tuberculum olfactorium. It is a zone of cells 
which are grouped into three sets, namely, first a more medial area of scattered cells ; 
secondly, an intermediate lying nearer the circumference of the section ; and third, 
an external area of large cells ( lat . ar. 1 , 2, 3). This zone, which I have carefully 
traced in an anterior and posterior direction, is clearly a continuation of the formatio 
pallialis. The term given to this area by Johnston, namely, the somatic area, does 
not, however, appear suitable. The stria medullaris (see p. 498) and the primordium 
