THE OPTIC THALAMUS 59 



Plate XXX. shows the outer margin of the optic thalamus adjacent to the internal capsule. 

 The object of the plate is to demonstrate the ' enormous number of fine neuraxons issuing 

 from the thalamus and entering the internal capsule. The thalamic fibres are shown in the 

 plate as passing from above downward and toward the left. The internal capsule fibres are 

 shown passing across the plate below. Among the latter, two long fusiform cells are seen 

 near the thalamus, with very long branches which subdivide at some distance from the cell. 

 Such cells are seen along the outer side of the thalamus in all sections and even in the 

 laminae medullares within the thalamus. They form a fourth variety of thalamic cell. The 

 fibres from the thalamus turn in a spiral manner on entering the capsule and become parallel 

 with the fibres of the capsule, but such turning cannot be shown by a photograph, which is 

 necessarily in one plane only. 



Von Monakovv has proven by experimental researches on animals and by studies in pathol- 

 ogy in man that the neurons in the thalamus must be considered as made up of two cat- 

 egories: (i) cells which lie in the thalamus and send out neuraxons which pass to and terminate 

 in the cortex; (2) neuraxons of cortical cells passing into the thalamus and terminating in 

 brush-like expansions about its cells. By means of these two sets of neurons the mutual 

 relation of the nuclei of the thalamus and the cortical areas, already described, are maintained. 

 He believes that the mutual relations of these neurons is secured by the intermediate action 

 of cells of Golgi's second type lying in the optic thalamus. I have not included such cells 

 in the diagram, Fig. 8. There are undoubtedly many other fibres leaving and entering the 

 thalamus to and from the lower levels of the central nervous system, as well as those which 

 enter it from the optic tracts. The latter are clearly connected with the pulvinar of the 

 thalamus and with the corpora geniculata. There is no reason to believe that the other 

 nuclei of the thalamus have any anatomical relation with the optic tracts. The relations known 

 to exist between the optic nerve, pulvinar, and occipital cortex may, however, be taken as in- 

 dicative of the relation between other parts of the thalamus and other subcortical and cortical 

 structures. These have been shown already in the diagram of the visual tract, Fig. 8. 



It is probable that the thalamus is the organ in which many automatic acts are coordi- 

 nated under the stimuli of various sensory impressions there united and brought into mutual 

 relation. Its exact function is, however, undetermined. 



