424 THE BRAIN OF MAMMALS, BY TH. MEYNERT. 



3. Without being connected with the substance of the optic 

 thalami, the posterior longitudinal fasciculus of the tegmen- 

 tum of the crus cerebri runs along the grey substance of the 

 central cavities first, of the third ventricle, and subsequently 

 of the aquseduct and fourth ventricle (figs. 245 253, L). The 

 central extremity of this fasciculus lies in a flat expanded gan- 

 glion (fig. 245, Z), beneath the fillet or loop of the crus cerebri 

 belonging to the lenticular nucleus (collar of the crus), corre- 

 sponding to the second stratum of the substantia innominata 

 of Reil, or anse pedonculaire of Gratiolet, a mass which stretches 

 above the optic tract transversely over the crusta (fig. 245, Schl, 

 Z). The cells of this ganglion extend into the external capsule, 

 the converging fasciculi of which (so far as their medulla does 

 not consist of connecting systems) spring from the cortex of the 

 upper edge of the fissure of Sylvius (Klappdeckel), and termi- 

 nate, not in the lenticular nucleus, which they only cover, but 

 in the ganglion of the peduncular loop or collar of the crus 

 (fillet). Occasionally a few fasciculi, either alone or mingled 

 with some interspersed fusiform cells (50 /n long and 15 ^ broad), 

 traverse the superficial strata of the third segment of the lenti- 

 cular nucleus. Besides its origin from the upper edge of the 

 fissure of Sylvius, the upper link of the projection system for 

 this ganglion also arises from the remaining walls of the Sylvian 

 fossa, from its medullary portions, which, proceeding from the 

 cortex of the insula, and from the temporal lobes, traverse the 

 claustrum. Fibrils from the lowermost parts of the infundi- 

 buluni also attach themselves to the inferior longitudinal 

 fasciculus, covering the pillars of the fornix internally, whilst 

 the greater part of the longitudinal fasciculus lies external to 

 the pillars of the fornix. 



i. Another mass of the grey substance of the central cavities 

 included in the optic thalamus is constituted by the descending 

 pillar of the fornix, as well as by the commencement of the 

 ascending, before this penetrates into the ganglionic mass of 

 the optic thalamus (fig. 246, Fd, Fa). 



According to Meckel, Arnold, Jung, and Luys, the descend- 

 ing crus of the fornix, before its entrance into this grey 

 substance, fuses with the anterior extremity of the stria cornea 

 (but surely not with the whole !) and with that of the brachia 



