INTERIOR SURFACE OF THE FORE-BRAIX. 103 



crosses. It has a free border anteriorly, though imbedded in the 

 corpus striatum (Fig. 32). Upon its medial surface rest the 

 thalamus, below and behind, and the caudate nucleus, above and 

 farther forward. It thus separates the thalamus and caudate 

 nucleus from the lentiform nucleus. A bend seen in horizontal 

 section near the middle of the superior lamina, called the genu, 

 divides it into a frontal part (pars frontalis) and an occipital 

 part (pars occipitalis} which tend slightly outward from the genu 

 and form an angle with each other of about 120 degrees. 



Motor Fibers of Superior Lamina (Figs. 32, 33 and 70). 

 The fibers of the genu and anterior two-thirds of the occipital 

 part of the internal capsule are very largely motor and constitute 

 the pyramidal tract. They may be traced from the motor area 

 of the cortex (Figs. 54 and 56) through the internal capsule and 

 the middle three-fifths of the basis pedunculi, and on down into 

 the spinal cord. They end in ramifications about the cell-bodies 

 in the gray matter of the cord and in the motor cerebral nuclei. 

 From these same spinal and cerebral nuclei other fibers rise which 

 constitute the motor part of the spinal and cerebral nerves. The 

 pars frontalis of the internal capsule contains a motor tract which 

 extends from the frontal cortex through the inner one-fifth of the 

 basis pedunculi to the nucleus of the pons and motor nuclei of 

 the cerebral nerves (Flechsig). It is the fronto-pontal tract 

 (tractus cerebro-cortico-pontalis frontalis}. 



Sensory Fibers of Superior Lamina (Figs. 32, 33 and 70). 

 In both parts of the superior lamina of the capsule there are 

 common sensory fibers which rise chiefly in the thalamus and end 

 in the somaesthetic cortex (Figs. 54 and 56). They convey ordi- 

 nary sensations. In the frontal part is the frontal stalk of the 

 thalamus, which ends chiefly in the caudate and lentiform nuclei, 

 though some of its fibers reach the frontal cortex. The tract is 

 relayed in the lentiform nucleus, whence it is continued to the 

 somaesthetic cortex by way of the parietal stalk, which is entered 

 high up near the corpus callosum. The pars occipitalis of the 

 superior lamina contains the parietal stalk of the thalamus, 

 which conveys ordinary sensations from the thalamus to the somaes- 

 thetic cortex, chiefly to the posterior central gyrus. 



