194 



VETERINARY PHYSIOLOGY 



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fAce 



III. Fibres passing outwards from the Discharging 

 Parts of the Cerebrum. 



The fibres coming from this area of the cortex are mixed 

 with the ingoing fibres from the thalamus ah-eady 



described. But they are 

 distinguished from them by 

 the fact that they get their 

 medullary sheaths at a late 

 date, so that they may be 

 traced right down into the , 

 cord as the pyramidal tract 

 in the following situations : — 

 1st In the corona radiata 

 (figs. 96 and 97). 



2nd. In the anterior two- 

 thirds of the posterior limb 

 of the internal capsule, the 

 face fibres lying to the front, 

 the arm fibres behind these, 

 and the leg fibres furthest 

 back (figs. 96 and 97). 



Srd. In the central part 

 of the crusta of the crus, 

 arranged from within out- 

 wards — face, arm, leg (fig. 97). 

 Hh. In the pons Varolii, 

 between the deep and super- 

 ficial transverse fibres. The 

 face fibres cross here (fig. 97). 

 Hence a unilateral tumour 

 in this situation may cause 

 paralysis of the face on one 

 side and of the limbs on the 

 other — a crossed paralysis. 



5th. In the anterior 



pyramids of the medulla 



at the junction of 



Fig. 96. — Diagrammatic horizontal 

 section through base of cerebral 

 hemisphere, showing (1) the out- 

 going fibres for the leg, arm, and 

 face springing from the cortex of 

 the central areas, passing through 

 the internal capsule between 

 the thalamus and the lenticular 

 nucleus. The face fibres cross in the 

 pons, the leg and arm fibres in the 

 medulla. (2) The incoming fibres 

 (fillet, eye, etc.) have cell stations 

 in the thalamus, and then pass on 

 to the cortex. 



oblongata. Most of them decussate 

 the medulla and spinal cord (fig. 97). 



