THE BRAIN. 31 



runs down anteriorly over the thalamus to the foramen of Monro, through which 

 it enters the lateral ventricle. Two large veins, the veins of Galen, pass down 

 near the middle line of the third ventricle to empty into the straight sinus. Pos- 

 teriorly, the choroid plexus follows the descending horn of the lateral ventricles. 

 The choroid plexus hangs from' the under surface of the velum interpositum, which 

 is a fold of the pia mater entering through the transverse fissure. The veins of Galen 

 run between the two layers of the velum interpositum. 



Turning now to Fig. 37, showing a somewhat deeper transverse horizontal 

 section, running through the corpus striatum and thalamus, it will be seen that to 

 the outer side of the corpus striatum and thalamus is a white layer constitut- 

 ing the internal capsule. It divides the corpus striatum into two parts, one to its 

 inner side, which projects into the lateral ventricle, called the caudate nucleus, and 



Degenerative area 

 Corpus callosum 



Nucleus caudatus 

 Apoplectic area 

 Internal capsule 



-Nucleus lentiformis 



Crura cerebri 



Pons 



Medulla oblongata 



FIG. 38. Showing the degenerative and apoplectic areas of the brain and the course pursued by the motor 

 fibres from the cortex, through the internal capsule, crura, pons, and medulla to the decussation, where they 

 cross the median line to supply the opposite side of the body. 



the other to its outer side, called the lenticular nucletis. To the inner side of the 

 posterior portion of the lenticular nucleus and internal capsule is seen the thal- 

 amus. To the outer side of the lenticular nucleus one sees other white fibres called 

 the external capsule. An apoplectic hemorrhage occurring in the lenticular nucleus 

 or internal capsule may push forward and rupture into the lateral ventricle. It may 

 go backward and involve the anterior portion of the thalamus and burst into 

 the third ventricle, and if it extends outward it involves the external capsule. Some- 

 times, if the hemorrhage is low down, it ruptures downward through the base of the 

 brain, showing itself, of course, at the anterior perforated space. Fig. 33 shows these 

 structures as seen in a medial section of the brain. 



In Fig. 38 there is a coronal transverse section of the brain, showing the course 

 of fibres of the internal capsule from the cortex of the brain through the corpus 

 striatum, between the lenticular and caudate nuclei : then, forming the crus cerebri, 

 the fibres pass through the pons and medulla to enter the spine, decussate, and 

 pass to the extremities. This constitutes the motor pathway from the cortex to the 

 extremities, and when it is injured in apoplexy, the extremities of the opposite side 

 are paralyzed. 



