CEREBELLUM. 407 



body, called the corpus dentatum or rliomboideum, or ganglion 

 of the cerebellum. This ganglion receives the greater part 

 of the corpus restiforme, and with the central medullary por- 

 tion in which it is found, is connected with the medulla ob- 

 longata, pons Yarolii, and cerebrum. Three processes on 

 each side establish this connection : 1. The inferior process 

 or peduncle, corpus restiforme^ which extends from the 

 posterior column of the medulla oblongata, to this central 

 portion of the cerebellum. 2. The anterior peduncle or crus 

 cerebellij which proceeds from the floor of the horizontal fis- 

 sure on either side, and passing forward and inward, meets 

 with its fellow of the opposite side to form the anterior layer 

 of the pons or great commissure of the cerebellum, and 3. 

 The superior peduncle, or processus a cerebello ad testes. 

 These are two white, thick, medullary bands, which are 

 traced from the corpus dentatum of each hemisphere, and 

 ascend above the crura cerebelli, to join the testes. They 

 form part of the lateral boundaries of the fourth ventricle, 

 and are connected to each other by the valve of Vieussens, 

 which together act as commissures, both between the cere- 

 brum and cerebellum, as well as between the hemispheres 

 of the cerebellum and the median lobe. 



The fourth ventricle generally described as belonging to 

 the cerebellum, is rather considered a ventricle of the me- 

 dulla oblongata. It is situated upon the posterior surface 

 of the medulla oblongata, having the pons in front, the 

 median lobe of the cerebellum behind, and its hemispheres 

 laterally. It appears as a considerable cavity of a quadri- 

 lateral shape, about an inch and a half in length, and of 

 nearly the same breadth. 



The superior angle of this ventricle leads into the aque- 

 duct of Sylvius; the inferior corresponds with the posterior 

 median fissure of the cord. 



On the anterior and inferior wall of this ventricle is a 

 median groove, distinct and sharp, and from its resem- 

 blance to a writing pen, has been called calamus scriptorius. 

 On either side are white striae, the linece transversce forming 

 the feathers of the pen and being the origin of the auditory 



