GENERAL ARRANGEMENT OF PARTS OF THE BRAIN 



533 



3. The mid-brain, which comprises th2 crura cerebri and the corpora 

 quadrigemina enclosing the aqueduct of Sylvius. 



4. The hind-brain, which comprises the pons Varolii, forming the floor 

 of the fourth ventricle, and the cerebellum, forming the roof. 



5. The ajter-b ain, the medulla cblongata or bulb. 



FIG. 371. Longitudinal and Vertical Diagrammatic Section of a Vertebrate Brain. Letters 

 as before. Lamina terminalis is represented by the strong black line joining Pn and Py. (Huxley.) 



PIG. 372. Base of the Brain, i, Superior longitudinal fissure; 2, 2', 2", anterior cerebral 

 lobe; 3, fissure of Sylvius, between anterior and 4, 4 f , 4", middle cerebral lobe; 5, 5', posterior 

 lobe; 6, medulla oblongata. The figure is in the right anterior pyramid; 7, 8, 9, 10, the cerebellum; 

 -K the inferior vermiform process. The figures from I. to IX, are placed against the corresppnding 

 cerebral nerves; ///. is placed on the right crus cerebri. VI. and VII. on the pons Varolii; X., 

 the first cervical or suboccipital nerve. (Allen Thomson.) X . 



