THE STRUCTURES AT THE BASE OF THE BRAIN. 93 



thalamus, bent around in the corpus candicans, and passed into 

 the fornix. The investigations of Gudden, however, have dis- 

 proved this ; therefore, its old name, fornix descendens, is not 

 justified, and it is now called, after its discoverer, the bundle of 

 Vicq d'Azyr.* Arising from the more anterior of the nuclei, 

 a little strand of fibres ascends toward the thalamus alongside 

 the last-described bundle, but soon changes its course and 

 passes backward, curving caudad until it reaches the tegmentum 

 back of the region of the corpora quadrigemina, where it 

 can be traced into ganglia that lie under the aqueduct of 

 Sylvius. This is called the tegmental bundle of the mammillary 

 body. 



If you will examine Fig. 46 or 49 you will see that the 

 thalamus lies directly upon the internal capsule. Farther back 

 this condition of things ceases. Here several small, gray, gan- 

 glionic masses are interposed between the capsule and the 

 thalamus. Into these ganglia numerous bundles of fibres radiate 

 from the nucleus lentiformis, the capsule, and the thalamus 

 itself. The posterior basal inter-brain region where this occurs 

 is called the regio subthalamica. The regio subthalamica w r as 

 first accurately known through the researches of Luys and 

 Forel, and later by the works of Flechsig and Wernicke. We 

 are, however, still far from a comprehension of the complicated 

 conditions which are presented to us in this little space, where 

 fibres of such widely different origin meet, interloop, and cross 

 each other, and where gray masses lie which are themselves in 



O V 



part permeated by a fine-meshed network of crossing and inter- 

 mingling medullary fibres. 



Fig. 54 shows a few details of a section through this 

 region. Below the thalamus is a rounded ganglion, the nucleus 

 ruber, the red nucleus of the tegmentum. External to it lies 

 the lenticular-shaped corpus subthalamicum (body of Luys). 

 You recollect the bundle of coronal fibres which we called the 



* Compare Fig. 42, where by dissection a perceptible loop is brought into view between 

 the two portions of the fornix in the corpus caudicans. 



