780 



THE CtNTRAL AXIS OF THE NERVOUS SYSTEM. 



flattened above and below, and comprised at their internal borders between the 

 corpora restiformia and the inferior face of the lateral lobes of the cerebellum, 

 to which they are strongly adherent by their superior face. These two plexuses 

 are joined by means of Renault's valve, which is united to them towards its 

 base. 



Sulci and lobules of the cerebellum.— On examining, in a general manner, all 

 the sulci which intersect the external surface of the cerebellum, we see that they 

 penetrate to very unequal depths in the substance of the organ, and that they 



Fig. 429. 



MEDIAN AND VERTICAL SECTION OF THE BRAIN. 



1, Section of the medulla oblongata ; 2, ditto of the pons V.arolii ; ditto of the crura cerebri ; 4, 

 ditto of the cerebellum, showing the arbor vita;; 5, posterior ventricle covered by the cerebellum ; 

 6, aqueduct of Sylvius ; 7, section of the valve of Vieussens (the figure and the line proceeding 

 from it are too much forward); 8, natis ; 9, internal extremity of the hippocampus; 10, section 

 of the pineal gland (it is as voluminous as it was in the specimen from which this drawing was 

 taken) ; 11, great vena Galeni, proceeding from the velum interpositum and choroid plexus, 12 ; 

 13, middle ventricle; 14, foramen of Monro; 15, common posterior foramen; 16, grey com- 

 missure; 17, anferiiir white commissure; 18, section of the c(ir[)us albicans; 19, ditto of the 

 pituitary gland; 20, interior of the pituitary stem communicating with the middle ventricle; 

 21, section of the optic chiasma; 22, ditto of the fornix; 23, ditto of the corpus callosum ; 24, 

 septum lucidum ; 25, cerebral convolutions; 26, olfactory lobule. 



divide it into successively decreasing segments, of which Figs. 429 and 432 may 

 furnish a sufficient idea. 



There is at first a certain number of principal lobules, which are divided 

 into secondary lobules ; and these, again, are in their turn separated into short 

 lamellae, representing the extreme limits of cerebellar lobulation. 



Leuret has counted 178 lamellse in a section of the middle cerebellar lobe of 

 the Horse. In this animal he found the largest number. 



2. Internal Conformation and Structure of the CEREB'ELLTrM. 



The cerebellum concure — by its inferior plane and the internal face of its 

 peduncles— to form the cavity already described as the posterior or cerebellar 



