36 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



irregular, roundish, ball-shaped body, the size of a cherry, which 

 is attached to the base of the inter-brain by a slender pedicle. 



The thalamus is slightly separated from the nucleus cau- 

 datus by a bundle of fibres, called the stria terminalis. On the 

 anterior portion of its surface the anterior tubercle is usually 

 seen as a rounded swelling. It corresponds to a separate gan- 

 glion within. Still another ganglion belonging to the thalamus 

 will be found if we follow up the white line which runs along 

 the median ridge of the thalamus (stria medullaris). This gan- 

 glion is a small, club-shaped mass lying far back, just in front of 

 the corpora quadrigemina, and is called the ganglion habcnulae. 

 From this there arises on each side a thin, white bundle of fibres 

 which passes to the pineal gland, the pedunculus conarii. The 

 gray mass of the thalamus is overlaid with white fibres (stratum 

 zonale), which, in part, pass to the optic nerve. A principal 

 point of origin for this nerve is a protuberance on the posterior 

 part of the thalamus, the pulvinar. Macroscopic observation 

 alone would place the source of the optic nerve in this ganglion 

 and in two nodules on its under side (corpus geniculatum mediale 

 and laterale). Between the thalami there extends a thin, gray 

 lamina, the middle commissure. I have never failed to find it 

 if the brain was carefully taken out. 



The nerve-tracts from the hemispheres which lie deep down 

 between them and the thalamus emerge, for the most part, 

 caudad of the thalamus from the main mass of the cerebrum. 

 They form thick strands, and lie exposed on the ventral surface 

 of the 'mid-brain, the corpora quadrigemina; taken together, 

 they are called the crura of the brain (pedunculi cerebri). 



Behind the pineal gland begins the roof of the mid-brain. 

 We regard the posterior commissure as the most anterior por- 

 tion of this roof, as, arising in the thalamus, it passes caudad 

 through the mid-brain. The corpora quadrigemina, which ap- 

 pear just behind this commissure, we shall examine later on. 



If the brain is opened from above, as we have done, only 

 the inner portion of the corpus striatum the nucleus caudatus 



