238 J. B. JOHNSTON, 
in size of the area olfactoria and parolfactoria in Reptiles as compared 
with Acipenser, and that the growth of the cortex in connection with 
this area has resulted in a marked upward flexure of the base of the 
fore brain. In Acipenser the base of the fore brain is parallel with 
the longitudinal axis of the whole brain, while in Reptiles it is nearly 
at right angles to the longitudinal axis. The pallial commissures 
(psalterium) which are situated in Reptiles dorsal to the commissura 
anterior, if present in Acipenser, would lie cephalad from the com- 
missura anterior in the region of the nuclei postolfactorii. It is from 
the cortex adjoining this region in Reptiles that the fibres of the 
fornix arise. In order to affirm the existence of a fornix in Aci- 
penser it would be necessary to find cells in this region which are 
not immediately, but secondarily, connected with the mitral cells and 
which send their neurites to the ganglia habenulae or the corpus 
mammillare. This has not been done (cf. page 235). However, I 
think there can be no doubt that a part of the cortex is developed 
in this region, and believe that it is represented by the associational 
cells in Acipenser. These probably correspond to the cortex lateralis 
of Reptiles. 
The second group of cells probably corresponds to the cortex dor- 
salis or medio-dorsalis of Reptiles (EDINGER, 96a). If it be admitted 
that these cells in reality represent any part of the cortex of higher 
Vertebrates, then we find here in progress the actual transformation 
of a membraneous pallium into a massive one. This amounts to 
demonstrative evidence in favor of the RABL-RÜCKHARD hypothesis. 
d) Commissura anterior. 
The elements entering into this commissure have been discussed 
in part in the above pages. In lower Vertebrates it consists of 1) 
ascending fibres from the hypothalamus to the epistriatum, 2) fibres 
from the olfactory lobe to the various olfactory nuclei in the fore 
brain, and 3) fibres crossing from the superficial cells of the corpus 
striatum (cortex lateralis) to the epistriatum of the opposite side. 
The hypothalamus constituent is either absent or unobserved in 
Mammals. The olfactory portion corresponds to the anterior or ol- 
factory horn in Mammals. The partially isolated portion of the 
olfactory bundle corresponds to the separate olfactory commissure 
of Petromyzon (EDINGER, 88). The cortico-epistriaticus portion 
corresponds to the pars corticalis in Reptiles or to the pars epistri- 
aticus, or perhaps to a combination of the two (EDINGER, ’96b, p. 148). 
