424 



PHYSIOLOGY 



hemispheres, from which it is separated by the velum interpositum 

 and by the ependyma, the epithelium completing the inferior wall of 

 the lateral ventricle in this region. It consists of three masses of 

 grey matter the anterior nucleus, the lateral nucleus (the largest 

 of the three), and the mesial nucleus. Its outer surface is in contact 

 with the layer of nerve fibres formed by the crusta of each crus cerebri 

 as it diverges from its fellow to pass up into the cerebral hemispheres. 

 Into this layer, ' the internal capsule,' fibres proceed from all 

 parts of the thalamus to pass to the cerebral cortex. The anterior 



FIG. 191. Transverse section through upper part of mid-brain. 

 Th, thalamus ; brs, brachium superior ; cqs, anterior (or superior) corpus 

 quadrigeminum ; cgi, cge, internal and external geniculate bodies ; /, fillet ; 

 s, aqueduct ; pi, posterior longitudinal bundle ; r, raphe ; ///, third nerve ; 

 nlll, its nucleus ; Ipp, posterior perforated space ; sn, substantia nigra ; 

 cr, crusta ; //, optic tract ; Jf , medullary centre of the hemisphere ; 

 nc, nucleus caudatus ; st, stria terrninalis. 



extremity of the thalamus, known as the anterior tubercle, forms a 

 marked projection into the lateral ventricle. In front of this, the 

 foramen of Monro leads from the third ventricle into the lateral 

 ventricle. This foramen is bounded anteriorly by a strand of fibres, 

 known as the ' anterior pillar of the fornix,' which lies just behind the 

 anterior commissure and forms a conspicuous feature in the anterior 

 part of the lateral wall of the third ventricle. It passes in the wall 

 down to the corpus mammillare. From the corpus mammillare a 

 well-marked bundle of fibres passes up into the optic thalamus to end 

 round the large cells in the anterior nucleus of the thalamus. The 

 posterior extremity of the thalamus forms a definite prominence, 

 the pulvinar. To the outer and back part of the pulvinar two bodies 



