558 Dynamic Theory. 



pass from the posterior side of the crura to the front side, as they pass 



through the pons varolii on the road from thetestes to the olivary bodies. 



The Optic Thalami ( which have been mentioned ) lie on the posterior 

 or motor tracts of the cerebral peduncles immediately in front of the 

 corpora quadrigemina and separated from them by a curved transverse 

 groove. They are intimately connected with the tegmentum or sensory 

 part of the crura cerebri. They are much larger than the corpora quad- 

 rigemina and are composed entirely of gray vesicular matter. There are 

 two projections from the thalami on each side ; the forward one is the 

 more prominent and is called the corpus geniculatum externum. The 

 hind one does not project so far and is called the corpus geniculatum 

 internum. This is connected backward by a band with the testis. The 

 anterior somewhat rounded end of the Optic Thalamus is called the an- 

 terior tubercle, and the posterior end is the pulvinar. Under and be- 

 tween the two sides of the Optic Thalami is a cavity called the third 

 ventricle. At its rear end this communicates with the aqueduct of sylvius, 

 and at its front end is an opening called the foramen of Munro ( also 

 called anterior common foramen ), which opens above the corpora striata 

 into the lateral ventricles. A band of gray medullary matter that joins 

 the two lobes of the thalami over the top of the third ventricle is called 

 the middle commissure of the brain. At the hind end of the optic 

 thalami is another transverse band, composed of white fibres which are 

 lost in the body of the thalamus on each side. This is the posterior com- 

 missure of the brain. It forms the hind terminus of the third ventricle. 



Corpora Striata. These bodies form the anterior part of the floor of 

 the cavities called the lateral ventricles, the optic thalami .occup} T ing the 

 middle part, while the cornu ammonis or hippocampus major passing 

 over the optic thalamus fills the reflected or descending prong or cornu 

 of the ventricle, to be further described hereafter. In shape the front 

 end of the corpus striatum is spherical or bulging, while in the rear it 

 runs tapering backwards and partly enclosing the sides of the optic 

 thalamus with a prolongation of medullary matter which terminates at the 

 deflection of the descending cornu of the lateral ventricle. Each of the 

 corpora striata is separated from the optic thalamus by a groove in 

 which lies a narrow medullary strip called the Taenia Semicircularis, or 

 Tenia Striata. This band running towards the front connects with the 

 Fornix at the foramen of Munro. At the same point the peduncles of 

 the Pineal Gland unite with the Fornix. 



The posterior ends of the corpora striata practically form the floor of 

 cavities called the lateral ventricles, of which the cerebral hemispheres 

 are the roof. They are connected with the motor or anterior fibres of the 

 crura cerebri, as the optic thalami are with the sensory fibres. These 

 two ganglionic bodies, therefore, occupy the same relative position to 



