24 
hornes selbst entsprechen, wie aus der weiteren Schilderung von HENLE 
hervorgeht.” 
The comparative method shows clearly and decisively the nature 
of the indusium and the striae Lancisii. For in the examination of 
a large series of mammalian brains all the intermediate stages will 
be found to show the gradual transformation of the supracommissural 
hippocampus of the marsupial into the thin supracallosal film of grey 
matter which is found in the cerebrum of the Primates and Cetacea. 
By means of schemata representing transverse sections through 
the dorsal commissure I propose to represent graphically three stages 
in the evolutionary process. 
The Metatherian type (Fig. 1). 
The following features are to be noted: 
1) A typical hippocampal formation lying above the “commis- 
sura dorsalis” (C. S.) on each side of the median plane. 
2) The “commissura dorsalis” is the commissura forni- 
cis being a direct band extending from the alveus (alv) of one 
hippocampus to that of the other. 
3) The “commissura dorsalis” is situated in a mass of grey 
matter, a thin film of which may often be detected upon the 
dorsal aspect of the commissure connecting the fasciae dentatae 
(F. D) of the two sides. This grey fibre may be called the 
“indusium verum” (ind). 
4) The remainder of the same grey mass which contains the com- 
missure may be seen below the latter constituting the homo- 
logue of the septum pellucidum (S) of man. 
5) In the “septum” there is a bundle of descending fornix fibres 
(d. f), which contribute to the formation of the columna fornicis 
and precommissural fibres of the same side. 
6) In the superficial part of the hippocampus opposite the “layer 
of pyramidal cells” (pyr) there are a large series of bundles of 
fibres (2) in the stratum lacunosum and stratum zonale which 
pursue a course for a variable distance in the long axis of the 
hippocampus. They may be called the “longitudinal asso- 
ciation-fibres” of the hippocampus. They arise mainly as 
“collaterals” of the axis-cylinder processes of the cells of the 
“layer of pyramids” (pyr) and terminate in the stratum zonale, 
stratum lacunosum and stratum radiatum (s. r) at a variable 
distance (in the longitudinal axis of the hippocampus) from their 
place of origin. Some of them, in the region of the subicu- 
