1380 



A MANUAL OF ANATOMY 



Openings in the Roof.— ^These openings are three in number — one 



median and two lateral. They are situated in the non-nervous 

 part of the roof — ^that is to say, the part formed by the ependymal 

 epithelium of the ventricle, covered by pia mater, called the tela 

 choroidea inferior; and they penetrate both of these layers fepi- 

 thelial and pia-matral). The median opening is known as the 

 foramen of Magendie, and is situated immediately above the obex. 

 The lateral openings, right and left, constitute the foramina of 

 Lusclilta. Each is situated in the roof of the corresponding lateral 

 recess, where that recess terminates. 



By means of these three foramina — ^foramen of Magendie and 

 foramina of Luschka, right and left — ^the cavity of the fourth 

 ventricle communicates with the cisterna magna of the cranial 

 subarachnoid space, which in turn is continuous with the dorsal 

 part of the spinal subarachnoid space. 



, Upper Quadrigeminal Body 

 , Lower Quadrigeminal Body 

 ^. Superior Peduncle of Cer«bellum 



Right Hemisphere of Cer» 



bellum (m oblique 



section) 



Strise Acusticae 



Fig. 578. — The Fourth Ventricle and Right Hemisphere of the 

 Cerebellum (in Section) (Hirschfeld and Leveill^). 



Choroid Plexuses of Fourth Ventricle. — ^These are two in number, 

 right and left. Each is a longitudinal inflexion of the pia mater 

 which forms the tela choroidea inferior, and it invaginates the 

 ependymal epithelium of the lower part of the roof of the ventricle, 

 by which it is covered on its ventricular surface. Each choroid 

 plexus consists of two parts — ^longitudinal and transverse, and the 

 two plexuses are disposed somewhat thus: "]f. The longitudinal 

 parts lie on either side of the median line, and extend upwards from 

 the region of the foramen of Magendie. Each transverse part ex- 

 tends outwards into the corresponding lateral recess of the ventricle. 



Development of Fourth- Ventricle. — ^The lower or bulbar part is 

 developed from the myelencephalon ; and the upper or pontine 

 part is developed from the metencephalon, these being the two 

 divisions of the rhombencephalon. 



