422 PHYSIOLOGY CHAP. 



The posterior lobe of Bolk is larger and includes all the rest of 

 the cerebellum. It can, however, be subdivided into four lobules, 

 two median and two lateral. 



(a) The first of the two median lobules, called lobulus simplex 

 by Bolk, becomes so wide in man that anatomists had distinguished 

 in it a declivium or median part, and the lobus quadratus superior 

 or lateral parts. To this Bolk restores the character of a single 

 median unpaired lobule. 



(6) The second of the median lobules is the lobulus medianus 

 posterior of Bolk, the so-called vermis interior. The single, un- 

 paired character of this organ is admitted by every one. 



(c) The two lateral lobules were termed lobuli complicati by 



Fia. 221. Inferior surface of cerebellum with pons Varolii and medulla oblongata. (Sappey, after 

 Hirschfeld and Leveille.) . 1, 1, inferior vermiform process ; 2, 2, median depression or 

 vallecula ; 3, 3, postero-inferior lobe of hemisphere ;. 4, amygdala ; 5, flocculus ; Q, bivcntral 

 lobe ; 7, pons Varolii ; 8, middle peduncle of cerebellum ; 9, medulla oblongata ; 10, 11, anterior- 

 part of great horizontal fissure ; 12, 13, smaller and larger roots of fifth pair of nerves ; 14, sixth 

 pair ; 15, facial nerve ; 16, pars intermedia ; 17, auditory nerve ; 18, glosso-pharyngeal ; 19, 

 pneumogastric ; 20, spinal accessory ; 21, hypoglossal nerve. 



Bolk, and include the remainder of the cerebellum. While the 

 other lobes develop in an antero-posterior line, so that the inter- 

 lamellar sulci all have a transverse or oblique direction, the 

 development in the lobuli complicati follows a twisted or spiral 

 line, and the interlamellary sulci consequently run in irregular and 

 even opposite directions. The schematic type which Bolk gives 

 for this lobule results from two loops back to back joined by an 

 isthmus that runs parallel with the median line. In the human 

 cerebellum there is an enormous development of the parts con- 

 tained in the first loop, which includes the lobuli semilunaris, 

 gracilis, and cuneiformis of the anatomists ; the isthmus is formed 

 by the tonsils ; the whole of the rest, which is rudimentary, consists 

 of the flocculus. 



This new morphological and phylogenetic view of the cere- 



