Nerves, Spinal Coed, Brain and Other Ganglia 83 



sulcus oculomotorius separating them, and lying in front of the upper 

 part of these, the corpora mamillaria [Fig. 67]. 



Still farther forward is the protuberance known as the tuber cine- 

 reum from which the infundibulum extends down to the pituitary 

 body (hypophysis) 12 [Fig. 66]. 



The mid-brain between the crura and the corpora quadrigemina is called 

 the tegmentum. The ventral portions of the crura are called crustae. 



The crustae of the crura are separate in the mid-brain. Above, the 

 tegmentum also divides, and each half of the brain stem enters a thala- 

 mus. The thalami are ovoid masses of gray matter, divided into three 

 nuclei, the nucleus anterior (or dorsal nucleus), the nucleus medialis and 

 the nucleus lateralis. 



Laterally to each thalamus are two nuclei (nucleus caudatus and nucleus 

 lenticularis) , which together form the corpus striatum. Between these 

 two nuclei a fan-shaped mass of nerve fibers (the internal capsule) runs 

 up from the crusta. Lying behind the corpus striatum is another sheet of 

 fibers; the external capsule [Fig. 70]. 



The dorsal projection of the thalamus is the pulvinar. Lying below 

 and outwardly to the pulvinar are the geniculate bodies (two on each 

 side), the external or lateral and the internal or medial [Fig. 69]. 



Above the thalami are the two hemispheres of the cerebrum which are 

 spread out over and behind the thalami and the mid-brain. The hemis- 

 pheres may be considered as ganglia, or groups of ganglia, the cells of 

 which are in the outwardly lying portions (the cortex) . 



Running between the hemispheres is a broad band of fibers, the corpus 

 callosum, and two other smaller bundles, the anterior and posterior 

 commissures. (Many bundles of association fibers connect the various 

 lobes of the same hemispheres). 



Growing forward from the under side of each hemisphere near the 

 brain stem is a long process, the olfactory tract (tractus olfactorius) at 

 the end of which is the enlargement called the olfactory bulb [Fig. 68]. 



THE COLUMNS AND TRACTS OF THE SPINAL CORD. 



In the ' white matter ' of the cord three pair of columns are distin- 

 guished for convenience of reference [Fig. 41]. 



1. The posterior columns, lying between the ' posterior horns ' of 

 the gray matter, and separated by the posterior fissure of the cord. 



12 By physiologists the terms " pituitary " body and " hypophysis " are loosely 

 used as equivalent. Embryologists however describe the pituitary body as made up 

 of the hypophysis and the infundibulum. 



