76 Anatomy of the Nervous System 



the peduncle of the mamillary body {peduncidus mamillaris, 

 tractus mamillo-peduncidaris). This fasciculus ascends from 

 the hindbrain along the ventral surface, just medial to the 

 pes pedunculi (Pis. XIW, X\\, XXVL). It enters the mamil- 

 lary body dorso-lateral to the column of the fornix and 

 bifurcates there, sending many transverse fibres dorsal to 

 the fornix into the medial nucleus, while the rest of the tract 

 passes ventrally into the lateral nucleus.^ It can be traced 

 back down the brain to about the level of the most posterior 

 roots of the oculomotor nerve, where it joins the medial 

 lemniscus, with which at least some of its fibres have evidently 

 ascended. The mamillary body also receives afferent fibres 

 from the tuberculum olfactorium, etc., through the olfacto- 

 hypothalamic tract. 



The efferent fibres of the mamillary body leave the 

 antero-dorsal part of the medial nucleus as a group of com- 

 pact bundles which form a conspicuous tract running an- 

 teriorly and dorsally to end in the anterior nucleus of the 

 thalamus (p. 82). This tract is the mamillo-thalamic tract or 

 bimdleof Vicqd'Azyr {fascictdtis mamUlo-tlialamicus) (Pls.X\\- 

 XX., XX\T.). Shortly before reaching its terminal nucleus, 

 it breaks up in the rat into many small scattered bundles, 

 so that it becomes much less evident than it is in the pre- 

 ceding part of its course. The early course of these fibres is 

 not straight, however, as is strikingly evident in sagittal 

 sections. They curve rapidly upwards until they are running 

 nearly xertically, when many of them bifurcate, the one 

 branch turning sharply forward in the mamillo-thalamic 

 tract, while the other continues its sweeping curve and takes 

 a posterior direction across the medial surface of the fasciculus 

 retroflexus and back to the dorsal nucleus of the tegmentum. 

 There, it has already been described as the mamillo-tegmental 



K\ few fibres from this tract continue forward into the tuber cinereum 

 in the rat. A lesion in the peduncle in this animal produces no descending 

 degeneration (Papez). 



