113 



b. The Nucleus Genidul atwn. — This nucleus is imbeidei 

 in the substance of the thalamus lateral to the nucleus striti 

 grisei. It is separated from the neurones of that group and 

 from the external surface of the brain by bundles of fibre- 

 tracts. In transverse section, this collection of neurones 

 appears as a broad band curving parallel with the li-nitans 

 externa (Pig. 84, n.gen.). 



The size of a neurone from the nucleus geniculatum is 

 considerably less than that of one from the nucleus strati 

 grisei, and the form is of the elongated instead of the radia- 

 ting type. Fibres from the opticus leave that nerve to form a 

 terminal zone on the periphery of the thalamus, and the den- 

 drites of these neurones extend out'fari into this zone, while 

 their axones take a course inward. The neurone, therefore, 

 comes to be drawn out in a direction approximately at right 

 angles to the limitans externa (Fig. 84, n.gen.). The cell- 

 body is rendered somewhat elongated by the processes taking 

 origin at its extremities. The interior of the cell is almost 

 wholly occupied by the nucleus, leaving but a scanty amount of 

 cytoplasm in the bases of the cell-processes (F'ig.63). The 

 chromatin is in the condition of a fine reticulum. The tigroid 

 substance is necessarily small in amount where there is so 

 little cytoplasm, embracing only a few scattering granules. 



Structurally considered, the neurones of the nucleus genic- 

 ulatum are little specialized, remaining in an embryonic condi- 

 tion, so to speak. Their functional value is also of a low 



