THE GENERAL FUNCTION OF THE CEREBRUM 661 



radiation. They emerge from the outer part of the pulvinar and external genicu- 

 late body. 



(6) The Fillet System of Fibers. This is the tract which enables the impulses 

 from the different sensory paths of the cerebrospinal system to reach the thalamus 

 and subthalamic region. 



(c) The Superior Cerebellar Peduncle. This tract connects the central ganglia 

 of the cerebellum with the thalamus and subthalamic region. Some of them may 

 pass directly through and around this structure to reach the region of the fissure 

 of Rolando. 



(d) The Auditory Radiation. These fibers extend from the internal geniculate 

 body to the temporal lobe. They traverse the posterior extremity of the internal 

 capsule under the lenticular nucleus. 



B. Efferent, (a) The Pyramidal Tract. These fibers arise in the motor area 

 of the cortex and pass through the corona radiata into the internal capsule. Here 

 they are grouped in the genu and anterior two-thirds of the posterior limb. In 

 their downward course they enter the crusta and pyramids of the pons and medulla. 

 Most of them cross the midline in the upper part of the spinal cord to enter the 

 crossed pyramidal tract. The others continue onward on the same side where they 

 form the direct pyramidal tract, but cross over gradually in the lower part of the 

 cord. 



(6) The frontopontine fibers take their origin in the cortex of the frontal lobes 

 and eventually gain the mesial extent of the crusta of the crus cerebri. They 

 terminate in the formatio reticularis of the pons or nucleus pontis. 



(c) The temporopontine fibers originate from the two upper temporal convolu- 

 tions and enter the outer extent of the crusta. From here they enter the pons, 

 where they terminate in the nucleus pontis and are brought into relation with the 

 middle peduncles of the cerebellum. This path, therefore, serves as the chief 

 efferent bridge between the cerebrum and cerebellum, the afferent connection 

 between these organs being represented by the fibers passing between the cere- 

 bellar cortex and dentate nucleus to the superior cerebellar peduncle, red nucleus, 

 optic thalamus and the cerebral cortex of the opposite side. 



The association system unites the different areas of the cerebral 

 cortex of the same side with one another. Some of these fibers merely 

 dip downward into the white matter to clear the bottom of the sulci 

 and to enter the cortex immediately adjoining, while others pass to 

 more remote regions. For this reason, these fibers are said to form 

 short and long association paths, the most prominent of which are the: 



(a) Uncinate fasciculus which connects the orbital convolutions of the frontal 

 lobe with the anterior segment of the temporal lobe. 



(6) Cingulum which passes between the anterior perforated space and the 

 hippocampal gyrus and temporal lobe. 



(c) Longitudinal superior fasciculus which forms the connection between the 

 frontal, perietal and occipital cortex. 



(d) Longitudinal inferior fasciculus which extends along the occipital and 

 temporal lobes. 



(e) Occipitofrontal fasciculus which is situated internally to the corona radiata 

 and next to the caudate nucleus. 



The commissural system consists of three chief bridges which unite 

 the two hemispheres, namely : 



(a) The corpus cattosum consists of fibers which arise in all parts of the cortex 

 with the exception of the anterior and posterior segments of the temporal lobes and 

 the olfactory bulb. They originate in cells of the cortex but may also be the 

 collaterals of certain projection axons. Having reached the other side, they arborize 

 extensively. 



