THE OPTIC THALAMUS 5I 



THE OPTIC THALAMUS 



THE optic thalamus consists of a large mass of gray matter, egg-shaped, which lies upon 

 the floor of each lateral ventricle, its upper and inner surfaces being free, its outer surface 

 lying against the internal capsule, and its lower surface being upon the base of the brain 

 and upon the tegmentum of the crus cerebri. Its connections with the other parts of the 

 brain are made partly through its base, and chiefly through the internal capsule. Upon 

 section either horizontally or vertically, it is evident to the naked eye that bundles of white 

 fibres enter it from the capsule, forming apparent divisions between the masses of gray matter. 

 These white bundles have been called the laminae medullares, and the various divisions of the 

 gray matter formed by the presence of these laminae have led authors to describe a number 

 of different nuclei in the thalamus. The most recent and most accurate description of these 

 nuclei has been given by von Monakow. 1 He describes the following separate masses of 

 gray matter in the thalamus, but admits that there is no absolute separation between these 

 nuclei at some parts of their circumference. That they are, however, distinct from one 

 another has been established by pathological investigations. Although very little is known 

 with regard to the function of these nuclei at present, von Monakow has shown that each 

 nucleus is in anatomical relation with a definite area of the cortex, and hence the separate 

 function of each nucleus can be in part deduced from the facts known regarding the function 

 of the area of the cortex to which it is joined. 



The position of these nuclei in the thalamus is shown in Fig. 9. 



The various nuclei are as follows: 



i st. The tuberculum anterius (to). This is a distinct hillock of gray matter lying upon 

 the upper free surface of the thalamus far forward and near to the median line. It consists 

 of a number of large nerve cells clustered together. The neuraxons of these cells pass 

 downward to the corpus mammillare at the base of the brain, forming the so-called bundle of 

 Vicz d'Azyr. They there meet the fibres of the fornix, which come from the hippocampus, 

 and thus bring the tuberculum anterius into anatomical relation with the cortex of Ammon's 

 horn. 



1 C. von Monakow, Archiv f. Psychiatric, Bd. XXVII. s. 640; 1895. 



