THE TEGMENTUM OF THE CRUS CEREBRI AND ITS GANGLIA. 425 



of the pineal gland. The upper hemisphere of the corpus 

 albicans (fig. 246, M) is imbedded with the roots of the fornix 

 in the basal mass of the grey substance of the central cavities. 



The corpus albicans or mammillare is a ganglion that is 

 included in a loop of the fornix, by which the passage of a part 

 of its fasciculi into the tegmentum is effected. The statement 

 made by Jung, that the fasciculi of the fornix only traverse the 

 substance of the corpus albicans, and that its medullary in- 

 vestment is derived from another source, is quite erroneous. 

 On the contrary, the descending crus of the fornix forms the 

 medulla of the external and posterior surface of this ganglion, 

 and, passing into the ascending crus, winds round to its internal 

 and anterior surface. 



By this means a portion of its fasciculi passes through the 

 ganglion, which consists of fusiform cells having a long diameter 

 of 20 30 ju, and a short of 9 /z, and from the upper border of 

 which (fig. 246, m) the fasciculus for the crus cerebri enters into 

 the tegmentum. The greater part of the fasciculus, however, 

 only touches the ganglion, and contains, especially in the ascend- 

 ing root of the fornix, closely arranged parallel nerve corpuscles 

 with a long diameter of 30 45 /a, and a short of 15 ju, which 

 appear to agree in size with the terminal cells of the ascending 

 crus in the anterior tubercle of the optic thalamus (fig. 247, 6r, 

 To). The peripheric extremities of the fasciculi of the fornix 

 are therefore connected with two forms of terminal cells, 

 of which the smaller lie in medullary corpuscles, the larger 

 in the course of the crus and the anterior tubercle of the optic 

 thalamus. 



The shape of the optic thalamus would be completely mis- 

 understood if we included the above-described grey substance 

 of the central cavities in its mass ; for it would then appear as 

 though the anterior extremity of the optic thalamus extended 

 down to the base of the cerebrum, whilst it really lies quite 

 remote from it. For the anterior extremity, the lowermost region 

 of the transverse section of the optic thalamus, rests not only 

 upon the crus cerebri, but also upon the wedge (in trans- 

 verse section) of the lenticular nucleus (fig. 245, a K, Z 1} L 2 , 

 Z 3 ). But still Burdach's description, that "inferiorly they are 

 seated like a pair of capitate processes on the crura cerebri," 



