THE BASAL GANGLIA OF THE CEREBRUM. 



805 



wanting as to the significance of the ganglia present in the pons. For 

 diagnostic purposes in man attention should be directed to the presence 

 of possible alternate hemiplegia. 



The quadrigeminate bodies or the midbrain. Destruction of the quad- 

 rigeminate bodies on one side in mammals, or of the optic lobe in birds, 

 amphibia, and fish, is followed by blindness, which may be situated upon 

 the same or upon the opposite side in accordance with the conditions of 

 decussation in the optic chiasm. Total destruction of the bodies on both 

 sides causes blindness in both eyes. As a result the reflex between irri- 

 tation of the retina and the oculomotor nerve is abolished, that is, the 

 pupils no longer contract after illumination of the retina. If the cere- 

 bral hemispheres alone are removed, the pupils still contract on light- 

 stimulation, as well as after mechanical irritation of the optic nerve. 

 Extirpation of the eye- 

 ball is followed by 

 atrophy of the contra- 

 lateral anterior quad- 

 rigeminate body. 



According to Bech- 

 terew the fibers of one 

 optic tract pass through 

 the brachium conjuncti- 

 vum anterius (Fig. 241) 

 into the external per- 

 iphery of the anterior 

 quadrigeminate body. 

 The fibers that decussate 

 in the chiasm (Fig. 240) 

 pass into the posterior 

 quadrigeminate body. In 

 accordance with this dis- 

 tribution are the symp- 

 toms of partial blindness 

 after destruction of an 

 anterior or posterior quad- 

 rigeminate body. Fibers 

 pass onward to the cortex 

 in the internal periphery 

 of the anterior quadrigem- 

 inate body. 



In animals deafness 

 has been observed to 

 develop after destruc- 

 tion of the posterior 



quadrigeminate body. Animals exhibit under such conditions diffi- 

 culty in phonation even to the point of loss. In man a paralyzing 

 lesion of the tegmentum or of the internal capsule is present in all 

 cases of midbrain deafness. Destruction of the quadrigeminate bodies 

 is followed further by disturbance in the perfect harmony of movement; 

 disorders of equilibration and incoordination of movement also occur. 



The cochlear nerve undergoes partial decussation in the posterior quadri- 

 geminate body and in the pons. The quadrigeminate bodies react to electrical, 

 chemical, and mechanical stimulation. The reports are contradictory, however, 

 as to the results of irritation. According to some observers dilatation of the pupil 

 on the same side takes place ; according to Ferrier the contralateral pupil dilates 

 first and later also the pupil on the same side. The irritation extends from the 



FIG. 264. Frontal Section through the Cerebrum: i ic, internal capsule; 

 2 Ik, nucleus lentiformis; 3 nc, caudate nucleus; 4 tho, optic thala- 

 mus; 5 cc, corpus callosum; 6 aec, external capsule; 7 cl, claustrum; 

 8 i, island. 



