234 A MANUAL OF ANATOMY. 



As the optic thalami grow upward they approach each 

 other and become united along their opposing surfaces. 

 This central bond of union later diminishes in extent, but 

 persists as the middle commissure. 



The fibres of the internal capsule turn downward and 

 backward under the optic thalamus ; thus the latter is said 

 to rest upon the former. 



The Internal Capsule. Figs. 32, 35, 45. 



From what has been said it will be apparent that this 

 part of the cerebrum is a mass of white fibres which pass 

 from the cortex and ganglia to the base of the brain, where 

 they appear as two rounded bundles of fibres under the 

 name of the crura cerebri. Fig. 29. 



From a vertical-transverse section the internal capsule 

 will be seen to pass upward and outward between the optic 

 thalamus on the inside and the lenticular nucleus on the 

 outside, then between the caudate and lenticular nuclei, and 

 then to radiate to the cortex of the brain. This radiation 

 of the fibres of the internal capsule is called the corona 

 radiata, and takes place to all parts of the cortex. Fig. 37. 



On a horizontal section the internal capsule presents two 

 portions or limbs, an anterior and posterior, united together 

 at an angle of about 113 degrees. The angle is the knee, 

 and is at the gap between the caudate nucleus and the optic 

 thalamus. 



The anterior limb lies between the caudate and lenticular 

 nuclei, the posterior between the optic thalamus and the 

 lenticular nucleus. As previously stated, the lenticular 

 nucleus has a narrow sheet of white fibres covering its ex- 

 ternal surface ; this is the external capsule. 



Again external to the external capsule is a plate of gray 

 matter the claustrum which is placed vertically, and in 



