APPLIED ANATOMY. 



Corpora Quadrigemina. The anterior corpora quadrigemina are associated 

 with sight, the posterior possibly with hearing and equilibrium. Note their prox- 

 imity to the cerebellum. 



Cerebral conex 



Spinal cord 



FIG. 47. The corona radiata or projection fibres which connect the cortex above with the thalamus, corpus striatum, 

 tegmental region, pons, medulla, and spinal cord below. These fibres go to form the internal capsule. 



Crura Cerebri. The crura cerebri transmit both sensory and motor impulses. 

 Note their proximity to the third nerve, as they are apt to be involved by the 



same lesions, thus accounting for paralyses 

 or sensory disturbances of the trunk or ex- 

 tremities accompanied by ocular paralysis. 

 Pons Varolii. The pons transmits 

 the motor or pyramidal tract, and also the 

 fifth, sixth, and seventh nerves. Implication 



c c // / \ of the seventh or facial nerve, together with 



the motor tract, has already been alluded to 

 (page 32). If the sixth or abducent nerve 

 is involved, the external rectus muscle on 

 that side will be paralyzed. If the fifth, or 

 trifacial nerve is affected, irritation of its 

 motor root may produce trismus or clench- 

 ing of the jaws, and interference with its 

 sensory root may cause anaesthesia of one 

 side of the face. 



THE CORONA RADIATA, INTERNAL 

 CAPSULE, AND MOTOR TRACT. 



The corona radiata is the bundle of white 

 fibres which spreads out like a fan and con- 

 nects the cortex of the brain with the basal 

 ganglia and spinal cord. Proceeding down- 

 ward from the cortex, the corona radiata be- 

 comes smaller and passes, in the form of a 

 band, between the lenticular nucleus on the 

 outside and the caudate nucleus and thal- 

 amus on the inside. This band is known 

 as the internal capsule. It transmits in its 

 anterior portion fibres from the pref rental or 

 higher psychical area ; then come the motor 



paths ; and still farther back, in the posterior third of the posterior portion, sensory fibres. 

 The functions of the external capsule, which lies to the outer side of the lenticular 



nucleus, are not known. 



Pyramidal 



decussation 



Lateral 



pyramidal tract 

 Direct 



pyramidal tract 



Spinal nerve 



FIG. 48. Diagram showing course and decussa- 

 tion of corticospinal (pyramidal) tract ; M, medulla; 

 P,pons; CP, cerebral peduncle; T, thalamus; C, L, 

 caudate and lenticular nuclei ; CC, corpus callosum. 

 (Piersol.) 



