420 THE PINEAL ORGAN 



ward into the crura cerebri. Immediately beneath the pineal body is the 

 roof of the aqueduct, containing the tecto-spinal and tecto-bulbar nuclei. 

 Around the aqueduct is the central grey matter and below it the various 

 nuclei of the third nerve, the nuclei of the fourth nerve, and the medial 

 longitudinal fasciculi (Fig. 279, p. 415), which if traced downwards are 

 found to be connected on each side with the superior olive, the nucleus 

 of the sixth cranial nerve, and that of the vestibular nerve. Ventral to 

 the nuclei of the third nerve are the red nuclei, the decussation of the 

 rubro-spinal tract, and the substantia nigra ; while dorso-lateral to the 

 red nucleus is the medial lemniscus. Ventral to the red nuclei is the 

 substantia nigra and near the outer borders of this are seen the medial 

 geniculate bodies. Passing upwards round the outer side of the crus 

 cerebri are the posterior cerebral and superior cerebellar arteries, with the 

 fourth nerve running ventrally and forwards between them. The basal 

 vein also, as mentioned previously, occupies the recess between the crus 

 cerebri and medial geniculate body on the inner side, and the tail of the 

 caudate nucleus, inferior horn of the lateral ventricle, choroidal fissure, 

 fimbria, and hippocampus are on the outer side. Finally the apex of the 

 pineal body is seen in a medial section (Fig. 280) to be in close relation 

 to the superior vermis of the cerebellum, and if the organ is enlarged it 

 may exert direct pressure on this and the superior peduncles or brachia 

 conjunctivae. Should a tumour of the pineal body enlarge forward into 

 the third ventricle it may exert pressure on the interpeduncular and 

 subthalamic regions and upon the optic thalami laterally. 



