490 
DR J. STUART THOMSON ON THE MORPHOLOGY OF THE 
An attempt may, however, be briefly made to compare the areas of neurones in 
the fore-brain, as described above, with the descriptions of other workers, but this 
can only be done and should only be accepted with caution owing to the extreme 
difficulty in some cases of arriving at any degree of certainty regarding the homo- 
logies of the parts described by different authors. The well-marked saucer- or 
cap-shaped area running latero-ventrally parallel with the margin of the hemisphere, 
the tuberculum olfactorium, is apparently identical with the cortex olfactoria of 
Edinger, the nucleus taeniae of Kappers, the nucleus post-olfactorius of Houser, 
the hypostriatum of Catois, and the area superficialis basalis of Johnston.* In the 
dorsal part of the hemisphere (pars pallialis of Gattpp) above the r zona limitans, in 
which I distinguish the formatio pallialis (lateral), the primordium hippocampi 
(dorsal), and the commencing corpus paraterminale (medial), Gaupp t describes and 
figures in the fore-brain of the frog the formatio pallialis lateralis, the formatio 
pallialis dorsalis, and the formatio pallialis medialis in corresponding order. In 
the same region Johnston distinguishes the primordium pallii somatici and the 
primordium hippocampi in various Selachian fore-brains. Further posteriorly and 
ventrally in the pars subpallialis of Gaupp he distinguishes the precommissural 
(paraterminal) body, but regards the latter as part of an area of central gray, which 
he terms the area olfactoria medialis. This last area, according to Johnston, lies 
below the zona limitans medialis, filling the “ septum.” The medial olfactory area 
I do not recognise as independent, regarding it as chiefly composed of the para- 
terminal body, which appears as a ventral extension of the primordium hippocampi, 
and partly of a more lateral part, a portion of the corpus striatum. This view I 
have not arrived at without very careful study of my sections. 1 have already 
indicated the position of the corpus striatum, situated in the ventral half of the 
hemisphere (pars subpallialis of Gaupp) dorsal to the tuberculum olfactorium. 
Johnston has described another area in this region, “the area olfactoria lateralis.” 
He writes, “this occupies a part of the lateral wall of the olfactory lobe, meeting 
the medial area at the olfactory peduncle and at the ventral angle of the ventricle.” 
In this paper I do not describe this area as distinct from the others which I have 
noted, as it appears to me (as no doubt Johnston will admit) that it has no sharp 
boundaries. It merges to a large extent dorsally into the formatio pallialis and 
ventrally into the corpus striatum. The “area olfactoria lateralis” apparently 
corresponds with the “ epistriatum ” of Kappers. 
From the condition described as occurring in the section figured in fig. 3 one 
gradually passes to the arrangement in which the two lateral hemispheres form one 
united mass with the velum transversum on the dorsal surface and a groove on the 
ventral surface. The arrangement of the areas of neurones at this stage is shown in 
* J. B. Johnston, “ The Telencephalon of Selachians,” Journal of Neurology and Psychology, vol. xxi, No. 1, 
February 1911. 
f Gaupp, Ecker’s and Wiedersheim’s Anatomie des Frosches, Braunschweig. 
