390 THE BKAIN OF MAMMALS, BY TH. MEYNERT. 



develop lateral processes, which appear to me to be in all in- 

 stances directed towards the free surface of the cortex, so that 

 there is no immediate connection of these cells with the pro- 

 jection system of the medulla. 



The medullary portion of the convolutions becomes collected 

 even within the cortex, beginning with the inner half of the 

 third layer, into clearly marked radial fasciculi, which, as 

 shown by sections, in .their course through the cell masses 

 divide them into columns. On one occasion I distinctly saw 

 the division of a medullary fibre in the cortex, or, in other 

 words, the formation of such a fibre from the processes of two 

 cells. On the other hand, such a plexiform arrangement of the 

 fibres of the medullary portion of the convolutions as has been 

 described by Stilling in the medulla of the cerebellum certainly 

 never occurs. Like the radial fibres, fibrse arcuatse are also, 

 though sparingly, found imbedded in the grey matter of the 

 cortex. I have never observed such an accumulation of them 

 as to cause them to form clear (in consequence of the absence 

 of pigment) concentric markings visible to the naked eye, such 

 as have been described by Kolliker. The medullary fibres of 

 the central convolutions are fine, varying, according to Kolliker, 

 from 2'6 to 6*7 fj. in diameter. The connective tissue of the 

 medulla consists of a reticulum of large connective-tissue 

 corpuscles with thick processes, and which, more rarely than 

 in the cortex, appear like free nuclei. These are elongated 

 parallel to the medullary fasciculi. In the fully developed 

 brain no finely granular substance appears to be present, 

 but daring the period of development it exists, and probably 

 occasions the more grey than medullary aspect of the imma- 

 ture organ. 



2. At the summit of the occipital region, and within the 

 neighbouring sulcus of the median surface, which, under the 

 name of sulcus hippocampi, forms a slight prominence with its 

 convexity directed towards the internal wall of the posterior 

 cornu, a different type of structure prevails. The pyramids 

 are no longer so abundant, but are replaced by granule-like 

 bodies. The former, which are of tolerably equal and moderate 

 size, enter into the composition of one (the second) layer only, 

 so that the characters of that which formed the fourth layer 



