CENTRAL LOBE. FOURTH VENTRICLE. 



525 



of grey matter' indented on the surface, and named the furrowed band. 

 Still further forward is the anterior pointed termination of the inferior 

 vermiform process, named the nodule, which projects into the fourth ven- 

 tricle, and has been named the laminated tubercle (Malacarne). On each 

 side of the nodule is a thin white lamella of a semilunar form, which is 

 attached by its posterior convex border, and is free and concave in front. 

 The outer ends of these lamellss are attached to the flocculi, and the inner 

 ends to the nodule, and to each other in front of that projection. The two 

 lamellae together constitute the posterior medullary velum, which has been 

 compared with the valve of Vieussens, the one being attached to the 

 superior extremity and the other to the inferior extremity of the middle 

 or vermiform portion of the cerebellum. This posterior velum is covered in 

 and concealed by the amygdalae, and cannot be properly seen until those 

 lobules have been turned aside or removed. 



The fourth ventricle. The space left between the medulla oblongata in 

 front and the cerebellum behind, is named the fourth ventricle, or ventricle 

 of the cerebellum. 



Fig. 357. VIEW OP THE Fig. 357. 



FLOOR OP THE FOURTH VEN- 

 TRICLE WITH THE POSTERIOR 

 SURFACE OF THE MEDULLA 

 OBLONGATA AND NEIGH- 

 BOURING PARTS (from Sappey 

 after Hirschfeld and Le- 

 veille). 



On the left side the three 

 cerebellar peduncles have been 

 cut short ; on the right side 

 the white substance of the 

 cerebellum has been preserved 

 in connection with the supe- 

 rior and inferior peduncles, 

 while the middle one has been 

 cut short. 



1, median groove of the 

 fourth ventricle with the fas- 

 ciculi teretes, one on each 

 side; 2, the same groove at 

 the place where the white 

 striae of the acoustic nerve 

 emerge from it to cross the 



floor of the ventricle ; 3, inferior peduncle or restiform body ; 4, posterior pyramid ; 

 above this the calamus scriptoriua ; 5, superior peduncle or processus a cerebello ad 

 cerebrum ; on the right side the dissection shows the superior and inferior peduncles 

 crossing each other as they pass into the white stem of the cerebellum j 6, fillet to the 

 side of the crura cerebri ; 7, lateral grooves of the crura cerebri ; 8, corpora quadri- 

 gemina. 



The cavity of this ventricle is of a flat rhomboidal shape, being contracted 

 above and below, and widest across its middle part. The anterior extremity 

 of the inferior vermiform process projects into it from behind, and higher 

 up it is covered by the Vieussenian valve. It is bounded laterally by the 

 superior peduncles, and by the line of union of the medulla oblongata and 

 the cerebellum. The upper end of the ventricle is continuous with the 

 Sylvian aqueduct or passage (iter) leading up to the third ventricle. 



The anterior surface or floor of the fourth ventricle is formed by the back 

 of the medulla oblongata and pons Varolii. It is shaped like a lozenge, 



