50 THE MEDULLA OBLONGATA AND PONS VAROLII. 



recess of the ventricle. Another thickening of the roof is seen at the apex of the 

 ventricle covering the point of the calamus scriptorius : this is named the olex. 



Two longitudinal vascular inflexions of the pia mater, known as the choroid 

 plexuses of the 4th ventricle, project from the roof into the cavity, one on either side 

 of the middle line, covered everywhere, however, by the epithelium of the roof. 

 Offsets from these pass also into the lateral recesses, from the apices of which they 

 emerge, encircled by a duplicate of the ligula, which was termed by Bochdalek the 

 cornucopia. The epithelial layer of the roof of the ventricle follows all the convolu- 

 tions of the choroid plexuses, but is nowhere pierced by them ; it is generally 

 described as the epithelium of the plexuses. 



The floor or ventral boundary of the 4th ventricle is marked at its widest 

 part, i.e., at the level of the lateral recesses, by seme transverse white lines, which 

 cross the grey matter of the floor, and are known as the strice medullares seu 

 acusticw (figs. 39, 40, 41, sir). 



These strife are caused by bundles of white fibres which emerge from the raphe, within 

 which they can be traced to the ventral surface of the bulb, and curve outwards over the 

 restiform body, where they are usually described as passing into the lateral root of the 

 auditory nerve. It is certain, however, that this is not the destination of most of the fibres 

 of the medullary strife, which are distinctly to be traced to the flocculus of the cerebellum 

 (fig. 49, p. 59). They vary greatly in development even upon the two sides of the same brain 

 (compare especially Bechterew, Neurol. Centralbl., No. 10, 1892). 



One bundle of these strife is sometimes seen, usually on one side only, taking a course 

 obliquely upwards and outwards, passing at the lateral boundary of the ventricle into the 

 middle cerebellar peduncle (aberrant 'bundle of stride medullares, Klangstab of Bergmann). 



The floor of the ventricle is bisected by a slight median groove. A little on 

 either side of this groove and immediately below the striae medullares, is a small 

 triangular depression (inferior fovea, fig. 40, './.), the apex of which extends only as 

 far as the striae, but the base is prolonged into two grooves extending one from 

 each angle. The inner of the two grooves passes with a slightly curved course 

 towards the point of the calamus scriptorius, and thus cuts off a pointed triangular 

 area, which is bounded mesially by the median sulcus, and the base of which is 

 turned towards the striae acusticse. This area (irigonum hypoglossi) is slightly 

 prominent, and constitutes the lower end of the fasciculus teres ; in it is the 

 prolongation of the tract of nerve-cells from which the roots of the hypoglossal 

 nerve take origin. The outer of the two grooves passes downwards with a slight 

 outward obliquity nearly to the lateral boundary of the ventricle, and marks off 

 externally another triangular area (irigonum acustici, La.), the base of which is also 

 directed upwards, where it can be traced into a prominence (best marked in children) 

 over which the striae acusticse course. To this prominence the name tuberculum 

 laterale seu acusticum has been applied, since the main part of the auditory nerve 

 arises in connection with it and with the triangular lateral area below it. 



Included between the two grooves is a third triangular area (irifjonum vagi), the 

 apex of which is at the inferior fovea, while its base looks downwards and outwards. 

 This area has a distinctly darker colour than the rest of the floor of the ventricle, 

 and especially than the trigonum hypoglossi on the inner side, which has a whitish 

 grey appearance, and it has accordingly been named the ala cinerea (a.c). Towards 

 the apex it is somewhat depressed, but below it is elevated into a distinct prominence 

 (eminentia cinerea). It contains the nucleus of the vagus, and superiorly, near the 

 inferior fovea, of the glosso-pharyngeal nerve. 



Above the strias acusticae the floor of the fourth ventricle is marked in 

 the middle of each lateral half by a distinct somewhat angular depression in a line 

 with the inferior fovea, from which it is separated by the eminence over which the 

 strias acusticae pass. This depression is termed the superior fovea (s.f.}. Between 

 it and the median sulcus is the prolongation of the funiculus teres, which is pro- 



