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A MANUAL OF VETERINARY PHYSIOLOGY 



pass to different parts of the brain, and out of the brain via the 

 bulb and cord. Fibres which pass from one part of the cortical 

 convolutions to another belong to the linking or association 

 system (Fig. 146) . Fibres which pass to the opposite side of the 

 brain via the corpus callosum belong to the commissural system, 

 while the masses sweeping out from the cortex and connecting 

 it with the mid-brain, pons, bulb, and spinal cord, belong to the 

 projection system. In Fig. 147 the projection system in the human 

 brain is shown. It is not wholly efferent — that is to say, it does 

 not consist entirely of motor fibres passing out to the pons, 

 bulb, and spinal cord. The motor tracts only form a part of the 



Fig. 146. — Association Fibres (after Starr). 



Human cerebral hemisphere seen from the side. A, A, association fibres between 

 adjacent convolutions; B, between frontal and occipital lobes; C, cingulum, 

 connecting frontal and temporo-sphenoidal lobes ; D, uncinate fasciculus be- 

 tween frontal and temporal regions ; E, inferior longitudinal bundle between 

 occipital and temporo-sphenoidal lobes ; O.T., optic thalamus ; C.N., caudate 

 nucleus. 



projection system, which in addition contains sensory, visual, 

 and auditory tracts, and fibres travelling from the frontal lobes 

 to the cerebellum. 



The Great Efferent or Motor Path in man is formed, as we have 

 just seen, from the large pyramidal cells in the cortical layer of that 

 portion of the cerebrum anterior to and bordering on the fissure 

 of Rolando, and travels backwards and downwards through the 

 corona radiata, internal capsule, and peduncles of the cerebrum 

 to the pons (Fig. 147, B). In this region are detached the motor 

 fibres connected with the cranial nerves, and these cross to the 

 opposite side of the brain. The larger mass sweeps onwards 

 through the bulb, and in the pyramids the system decussates, 

 the fibres crossing to the opposite side of the cord. In the cord 



