660 



THE CEREBRUM 



(6) Those which unite different parts of the same hemisphere 

 with one another, and 



(c) Those which extend from one hemisphere to the other. The 

 first group forms the so-called projection system, the second, the 

 association system and the third, the commissural system. Naturally, 

 each area of the cortex must be equipped with two sets of fibers, one 

 of which conducts away from it and the other toward it. In the case 

 of the projection system, the terms of afferent and efferent may be used 



FiQ. 330. — Schema of the Projection Fibers of the Cerebrum and of the Peduncles 

 OP the Cerebellum; Lateral View of the Internal Capsule. 

 A, Tract from the frontal gyri to the pons nuclei, and so to the cerebellum (frontal 

 cerebro-cortico-pontal tract) ; B, the motor (pyramidal) tract; C, the sensory (lemniscus) 

 tract; Z), the visual tract; E, the auditory tract; F, the fibers of the superior peduncle 

 of the cerebellum; G, fibers of the middle peduncle uniting with A in the pons; H, 

 fibers of the inferior peduncle of the cerebellum; J, fibers between the auditory nucleus 

 and the inferior coUiculus; K, motor (pyramidal) decussation in the bulb; Vt, fourth 

 ventricle. The numerals refer to the cranial nerves. {After Starr.) 



to distinguish these fibers from one another, but this terminology 

 is not applicable to the association and commissural systems, because 

 these fibers establish communication between different central parts and 

 do not possess a true motor or sensory function. The projection system 

 is made up of the following afferent and efferent tracts: 



A. Aferent. (a) Thalamocortical. — These fibers arise in the gray matter of all 

 parts of the optic thalamus and radiate outward to every area of the cerebral cor- 

 tex. In accordance with their distribution, they are grouped in the form of a 

 frontal, parietal, occipital and ventral stalk. Those forming the first group, do not 

 invariably pass directly to the frontal lobes, but may end in the caudate and 

 lenticular nuclei. Those destined for the occipital lobes, form the so-called optic 



