. THALAMI-OPTICI. 



415 



about an inch and a half long, and three quarters of an inch 

 in breadth and depth. They are convex superiorly and in- 

 ternally, and form the floor of the lateral ventricles. They 

 are separated in front by the teenia semi-circularis, from 

 the corpora striata, and are connected behind to the tuber- 

 cula quadrigemina ; on the posterior and inferior free por- 

 tion two rounded eminences are observed, of a grayish color, 

 called corpus geniculatum, ex- 

 ternum and internum. The op- 

 tic nerves are connected with 

 these eminences. A third tu- 

 bercle is spoken of, situated 

 above the corpora geniculata, 

 and called the tuberculum pos- 

 ter ius superius. 



The structure of the thalami 

 is medullary without, and a 

 mixture of white and gray mat- 

 ter within, forming a plexi- 

 form arrangement. The fibres 

 are traced to the olivary or 

 sentient tract with which they 

 are continuous, also to the 

 testes by the processes a cere- 

 bello ad testes, and to the posterior and upper part of the 

 crura cerebri. From their external surface these fibres ex- 

 pand into the hemispheres. On their internal and upper 

 surface is seen the long peduncle of the pineal gland, and 

 at their anterior part they are connected to the descending 

 crura of the fornix, to the tuber cinereurn, and corpora 

 albicantia. 



These thalami have been called, as stated, the great pos- 



FIG. 117 represents a horizontal section of the brain. / Corpus callosum. 

 g Raphe in its centre, h Lines) transversae. i Centrum ovale of Vieussens. 

 j Cortical portion of cerebrum, fc Medullary portion of cerebrum. I Lateral 

 ventricle, m n o Its anterior, middle, and posterior cornua. p Corpus stria- 

 turn, q Thalami nervi optici. r Linea semi-circularis. s Hippocampes major. 

 t Pes hippocampi, u Taenia hippocampi, v Hippocampus minor, to Plexus 

 choroides. 



