408 J. B. JOHNSTON 



In the bat also the stria mediahs is made up of precommissural 

 fibers and runs independently of the fascia dentata, separated 

 from it by the fimbrio-dentate sulcus (fig. 43). Caudally the 

 fibers pass into the lateral part of the nodule of cells at m, and 

 are lost. Probably they turn laterad here in the hippocampal 

 commissure. 



The above facts seem to show conclusively that the indusium 

 and stria lateralis Lancisii are strictly vestiges of the hippocampus 

 and fascia dentata as those exist in the marsupials. The stria 

 medialis, however, is a separate structure present in the mar- 

 upial and comparable with the fimbria bundle in the reptiles. 

 Professor Smith ('97, p. 85) speaks of the stria medialis as ''the 

 fimbria of the dorsal hippocampus." It together with the pallial 

 commissure belongs in the septum or undeveloped hippocampal 

 primordium. The stria medialis is strictly a part of the fornix 

 longus as defined by Elliot Smith ('97, p. 88) but differs from all 

 the other fibers of the fornix system in that it does not pierce 

 any part of the pallial commissure complex in order to reach 

 the hippocampus. This is recognized by Elliot Smith in the 

 passage referred to, which reads: 



From this account of the arrangement of fibers in the ox-brain, it 

 is evident that all the longitudinal uncrossed fibers of the fornix break 

 through some part of the great dorsal commissure (psalterium, splenium, 

 or corpus callosum, as that term is generally understood) in order to 

 reach the septum. These fibers constitute the true fornix longus. The 

 fornix superior consists of those fibers of the fornix longus which do 

 not pass through the main mass of the psalterium, but break through 

 a commissure of non-hippocampal or a mixture of the latter and hippo- 

 campal fibres (i.e., corpus callosum and its splenium). 



A few fibers of the fornix do not pass through any commissure. In 

 the marsupial (fig. 4 a) these fibers spring directly from the most ante- 

 rior part of the hippocampus, and pass downwards to their destinations 

 in front of the commissures. The corresponding fibers in the higher 

 mammal (fig. 2 a) become pushed forward by the extending genu cor- 

 poris callosi, but their essential disposition is unaltered, i.e., they spring 

 from the anterior extremity of the stria mesialis Lancisii. 



This statement requires modification in that the stria medialis 

 is connected with the caudal as well as the rostral part of the hip- 

 pocampus. The opossum and the bat show this conclusively. It 

 is probably for the very reason that the stria medialis is related 



