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HUMAN ANATOMY. 



lucidum and the olfactory area, and (2) cortico- habenular fibres, which spring from 

 the cortical cells within the hippocampus or the adjacent region, and by way of 

 the fornix and its anterior pillar are carried to the fore-end of the thalamus, whence 

 they pass backward within the medullary stria. (3) Other thalamo-habenular fibres 

 also probably join the stria medullaris from the interior of the thalamus. Whilst many 

 of the fibres composing the stria end around the cells of the ganglion habenulae, 

 some continue backward, without interruption, within the strand known as the 

 peduncle of the pineal body, cross to the other side in the bundle bearing the 

 name, commissura habenulae, and end in relation with the cells of the opposite 

 habenular nucleus. The ganglion habenulae (Fig. 970), in turn, gives origin to 

 an important bundle, the fasciculus retroflexus of Meynert, which arches down- 

 ward and backward, passing at first between the central gray matter of the third 

 ventricle and the thalamus proper, and later to the medial side of the red nucleus, 

 to reach the base of the brain, and for the most part to end around the cells of the 

 interpeduncular ganglion. This nucleus, which in many animals is a well-defined 

 collection of cells, in man is represented by a more scattered median cell-group 

 within the posterior perforated substance close to the anterior border of the pons. 

 The fasciculus, also termed the habenulo- peduncular tract, receives contribu- 

 tions from the ganglion habenulse of both sides, some fibres having crossed in the 

 habenular commissure ; although the majority of its fibres end, mostly crossed, in 

 the interpeduncular ganglion, not a few may be traced farther caudally within the 

 tegmentum of the brain-stem (Obersteiner), as may also the fibres from the cells 

 of the ganglion interpedunculare. 



The Pineal Body. The pineal body (corpus pineale), also often called the 

 epiphysis, is a cone-shaped organ, from 8-10 mm. in length, attached to the 

 posterior extremity of the roof of the third ventricle. It is slightly compressed from 



above downward and 



FIG. 971. rests, with its apex 



pointing backward, on 

 the dorsal aspect of the 

 mid-brain in the trian- 

 gular pineal depression 

 between the superior 

 corpora quadrigemina 

 (Fig. 966). Its base, 

 as its anterior end is 

 called, is attached 

 above to the commis- 

 sura habenulae, from 

 which on each side a 

 narrow but distinct 

 ric'^e, the pineal stalk, 

 curves forward to be- 

 come continuous with 

 the stria medullaris. 

 Pelc >w, i'.i base is united 

 with the posterior c< in- 

 missure of the brain 

 overlying the entrance 

 into the Sylvian aque- 

 duct. Between the 



habenular and posterior commissures a small pointed diverticulum, \\\v pineal recess, 

 extends from the third ventricle for a very short distance into the pineal body, 

 and thus recalls the early condition in which the organ is developed as a tubular 

 outgrowth in the roof-plate of the diencephalon. This relation to the thin ventricular 

 roof the body retains, its apex later becoming closely surrounded by and embedded 

 within the loose vascular tissue of the pia mater. 



The structure of the pineal body, as seen in cross-section ( Fig. 971), includes 

 a reticular framework of connective tissue trabeculae, whose meshes are filled with 



<$$ 



Connective 



ti-siir septa 



Section of pineal body showing calcareous concretions or brain-sand. X 130. 



