.,! 8 NORMAL HISTOLOGY. 



mic processes extend vertically into the outer part of the zone of 

 pyramidal cells, as well as laterally within the molecular layer ; their 

 axis-cylinder processes, on the contrary, are directed towards the 

 peripheral nerve-fibres, among which they end. 



7. The lamina medullaris involuta, constituting the outermost 

 layer of the convolution, lying next the fascia dentata, from which it 

 is separated by the intervening hippocampal fissure and its pial fold. 

 This layer corresponds to the greatly thickened outer zone of the 

 usual cortex, and is largely made up of tangential nerve-fibres 

 which proceed from the gyrus hippocampi, together with numerous 

 terminal fibrillae derived from the processes of ganglion-cells 

 situated in neighboring strata. 



The fascia dentata must be regarded as the projecting thickened 

 and specialized free edge of the cortical gray matter, lodged 

 within the hippocampal fissure, which it almost fills. The divisions 

 recognizable in this structure, from within outward, are 



1. The nucleus fasciae dentatae, which comprises an oval area 

 containing nerve-fibres continued from the alveus and numerous 

 ganglion-cells. The latter include three varieties of irregularly- 

 disposed elements, the pyramidal cells proper, the representatives 

 of the similar conspicuous constituents of the cornu Ammonis, the 

 polymorphous cells, possessing very numerous processes, and the 

 fusiform cells. 



2. The stratum granulosum, distinguished as a conspicuous 

 band of brilliantly staining small pyriform nervous elements, 

 whose protoplasmic processes extend towards the periphery, while 

 the axis-cylinder fibrils in general pass centrally. 



3. The stratum moleculare, consisting of a broad reticulated 

 zone of neuroglia, which contains numerous capillary blood-vessels, 

 a few scattered cells, and the extensions of the processes of the nerve- 

 cells ; it almost completely encloses the stratum granulosum, and is 

 itself covered by 



4. The stratum marginale, an extremely thin sheet of medul- 

 lated nerve-fibres representing the outer medullary layer of the 

 cornu Ammonis, of which it is the direct, although attenuated, con- 

 tinuation. 



The fimbria receives the fibres constituting the alveus, and is com- 

 posed entirely of bundles of medullated nerve-fibres, together 

 with the intervening connective-tissue septa ; the thick fibre-bundles 

 extend longitudinally, and are continued into the tracts of the posterior 

 pillar of the fornix. 



The septum lucidum represents a rudimentary cortex due to 

 the arrest of development following the isolation of this part of the 

 wall of the cerebral vesicle by the growth of the corpus callosum. 



