THE OPTIC THALAMUS 53 



nuclei and extends from the anterior backward to the posterior limit of the thalamus, lying 

 very near to the lower portion of the internal capsule. Von Monakow divides this into four 

 sub-nuclei, whose boundaries from one another are very indistinct, but whose independence is 

 assured by the results of degeneration. The anterior part of the ventral nucleus is in 

 anatomical relation with the frontal lobe of the brain in part. The remaining three parts of 

 the ventral nucleus are in relation with the portion of the cortex which lies near the fissure 

 of Sylvius, namely, the operculum, both central convolutions, and the gyrus supramarginalis. 

 The cells of this nucleus are shown in Plates XXVII. and XXVIII. 



5th. The pulvinar of the thalamus is the large collection of gray matter lying free upon 

 its posterior and superior surface, and manifestly connected with the optic tract (pulv in 

 Fig. 8). This lies behind the lateral nucleus and above the posterior part of the ventral 

 nucleus. It is in direct relation with the occipital lobe of the brain. Upon its posterior 

 and under surface two distinct hillocks of gray matter can be made out by the naked 

 eye ; namely, the corpus geniculatum externum (cge) and internum (cgi), Fig. 8. The corpus 

 geniculatum externum is directly related to the occipital cortex, as are the pulvinar and anterior 

 corpus quadrigeminum. The corpus geniculatum internum is in relation with the first and 

 second temporal convolutions, as is also the posterior corpus quadrigeminum. 



6th. The posterior nucleus (pn in Fig. 8). A small mass of gray matter belonging to 

 the thalamus lies beneath the pulvinar between the two corpora geniculata. This nucleus is 

 connected with the cortex lying between the temporal and occipital areas. 



The ganglion habenulae is a small collection of cells forming a distinct hillock on the median 

 surface of the thalamus and giving origin to the fibres which pass backward to the pineal gland. 

 The cells of this nucleus are shown in Plate XXIX. 



Von Monakow affirms that the tracts connecting these various nuclei with their respective 

 portions of the cortex are made up of two sets of fibres. One set has its origin in the 

 cells of the thalamus and its termination in a brush-like expansion about the cells of the 

 cortex. The other set arises from the pyramid cells of the cortex and ends in brushes 

 within the thalamus. Such a double set of fibres has already been shown in Fig. 8, con- 

 necting the pulvinar with the occipital cortex. To establish a further relation between the 

 impulses passing over these double tracts, von Monakow believes that in the thalamus there 

 lie many cells of Golgi's second type, an assertion which the investigations of Marchi confirm. 



There are several varieties of cells in the optic thalamus, and these are shown in Plates 

 XXV. to XXIX. 



Plate XXV. shows a form of cell present in many parts of the thalamus, but especially 

 characteristic of the median and lateral nuclei. These cells have a spherical body from which 



