THE TEGMENTUM OF THE CRUS CEREBRI AND ITS GANGLIA. 441 



division of the peduncle of the pineal gland extends in the foetus 

 of Man, and as a persistent condition in the adult state of many 

 Mammals, through the centre of the pineal gland itself (Luys). 



The presence of true commissural fibres of the posterior 

 commissure is also admitted by Burdach and Arnold. 



The pineal gland has often, but very incorrectly, been com- 

 pared with the Hypophysis cerebri. Luys still continues to 

 regard it as a continuation of the grey matter of the middle 

 ventricle. According to the more accurate statement of Arnold, 

 however, it is separated from the latter by its medulla. It is 

 to be regarded as a ganglion which, similarly constituted to 

 that of the peduncle of the gland, is, like the latter, continuous 

 on the one hand with the medulla of the hemispheres, and 

 on the other, by means of the posterior commissure, with the 

 crus cerebri. It may consequently be considered a ganglion 

 of origin of the tegmentum. It is composed of two forms of 

 cells, one of which has a diameter of 15 //, whilst the other 

 is much smaller, and does not exceed 6 /* ; in structure it is 

 distinguished from other cerebral ganglia only by the close 

 aggregation of its cells. In the peduncle of the pineal gland 

 the dense rows of cells alternate regularly with medullary 

 layers, and frequently exhibit an appearance similar to the 

 granule and medullary layers of the bulbus olfactorius. The 

 admixture of these medullary layers, and the constant presence 

 of processes from the cells, compel us to regard the latter 

 as nerve corpuscles. Their close arrangement is common to 

 them and to the stratum corporum arctorum of the cornu 

 Ammonis, and this with their minute size is common to the 

 olfactory lobes, the cortex of the cerebellum, and certain accu- 

 mulations in the grey substance of the corpora striata. The 

 latter however contains, in addition, dense masses of larger 

 nerve corpuscles. 



The convergence of the fasciculi of the projection system 

 proceeding from the cortex of the cerebrum to the corpora 

 quadrigemina is effected through the brachia of the nates 

 (fig. 249, Bs) and the brachia of the tesfces (figs. 249, Bi; 250, *). 

 The brachium of the nates traverses the thalamus just above 

 the corpus geniculatum, in consequence of which a triangular 

 region of the transverse section of the optic thalamus is in- 



