XXXIII] THE MID-BRAIN AND INTER-BRAIN 269 



14. Section through the brain just in front of the 

 posterior commissure and through the tuber cinereum 

 (cat). Note 



The 3rd ventricle above and below the soft com- 

 missure. 



The inner capsule, a thick band of fibres, for the 

 most part obliquely cut, lying on the lateral side of 

 the optic thalamus ; its ventral part is continuous with 

 the pes. The anterior end of the e. c. g. may be 

 imbedded in it. 



Numerous bundles of fibres connecting the optic 

 thalamus and the inner capsule. The lateral and the 

 median nuclei of the thalamus are separated from one 

 another by a thin layer of white fibres, the internal 

 stria medullaris. 



In the curve of the inner capsule, dorsally of the 

 thalamus a small patch of grey substance, the tail of 

 the nucleus caudatus. 



Ventro-laterally of the pes a little grey substance with nerve fibres, 

 the ansa lenticularis, and outside this on the surface, the optic tract. 



The triangular lenticular nucleus, continuous with the ansa lent, 

 and bounded laterally by the outer capsule. 



On the inner side of the pes a layer of grey substance, the 

 corpus subthalamicum, occupying approximately the position formerly 

 occupied by the substantia nigra. 



Dorsally of the corp. subth. a little grey substance with nerve 

 fibres, the zona incerta: bounded dorsally by a line of white 

 substance the external stria medullaris running from the inner 

 capsule and extending nearly to the mid-line. This forms the dorsal 

 boundary of the subthalamic region. 



Near the ventral surface and near the mid-line, a transversely cut 

 bundle of fibres, the anterior pillar of the fornix ; dorsally of this 

 obliquely cut fibres, the mammillo-thalamus bundle or bundle of 

 Vicq d'Azyr. 



