74 Anatomy of the Nervous System 



column of the fornix, and there may be also a small lateral portion passing 

 up lateral to the fibres of the internal capsule. 



(2) Tractus olfactohabenularis anterior — the largest component in 

 the rat. The fibres arise in the tuberculum olfactorium and pass back- 

 ward with those of the medial forebrain bundle (p. 97) to the level of the 

 optic chiasma, where they turn dorsally. 



(3) Tractus septohabenularis — made up of fibres from the entire 

 septal region in the broad application of that term (p. 93), especially from 

 the portion near the anterior commissure. 



(4) Tractus corticohabenularis medialis — composed of fibres arising in 

 the hippocampus and passing through the fimbria and column of the 

 fornix. They leave the latter for the stria medullaris when these structures 

 pass close to each other near the anterior commissure. They are drawn 

 on the lateral surface of the column of the fornix in Plate XXI, but are not 

 named. 



(5) Tractus corticohabenularis lateralis — fibres coming from the 

 pyriform lobe, nucleus of the lateral olfactory tract, and tuberculum 

 olfactorium running dorsomedially and converging with component (2) 

 to enter the stria medullaris (PI. XX., sma). 



(6) Tractus thalamohabenularis — consisting of fibres from the anterior 

 thalamic nucleus running through the stratum zonale thalami (the thin 

 superficial fibre layer) into the stria medullaris. 



(7) Tractus striohabenularis — fibres between the stria medullaris and 

 the medial part of the globus pallidus (p. 106) — connections unknown. 



(8) Imperfectly known connections between the habenula on the one 

 hand and the thalamus and the midbrain on the other. 



Apparently not included in this classification is (9) the stria medullaris 

 bundle of the stria terminalis which arises in the pyriform lobe, the nucleus 

 of the lateral olfactory tract, and the tuberculum olfactorium, according 

 to Johnston, runs through the stria terminalis, and joins the stria medullaris 

 near the anterior commissure. 



Gurdjian has recently confirmed for the rat the description of com- 

 ponents (1) — (5) and (9). He describes hypothalamic fibres in component 

 (1) and intimate synaptic relations between components (3), (4) and (9) 

 and the bed nuclei of the anterior commissure and the stria terminalis. 



In the stria medullaris, components (3) and (4) lie dorsally, (4) medial 

 to (3), and components (1), (2) and (5) ventrally and medially, (1) being 

 most ventral. 



Many of these connections are indicated in Fig. 4. 



The efferent fibres of the habenula take up a position 

 ventral to the nucleus, where they descend to near its pos- 



