CHAPTER XIII 



THE CEREBELLUM 



DEVELOPMENT OF THE CEREBELLUM 



THE dorsal border of the alar lamina occupies a lateral position in the rhom- 

 bencephalon and, as a result of the development of the pontine flexure, acquires 

 a V-shaped bend at the apex of which is the lateral recess of the fourth ventricle 

 (Fig. 137, A). This dorsal border becomes everted and forms a prominent 



Mid-brain 



Cerebellum 



Lateral recess 



Rhombic lip 



Corpora quadrigemina 

 Cerebrum 



A nlage of 

 vermis 



Lateral lobe of 

 cerebellum 



Rhombic lip 



Lateral lobe of cerebellum Lobules of vermis 



Obex 



Flocculus 



Uvula 



Nodulus 



Fig. 137. Dorsal view of four stages in the development of the cerebellum: A, of a 13.6 

 mm. embryo (His); B, of a 24 mm. embryo; C, of a 110 mm. fetus; D, of a 150 mm. fetus. (Pren- 

 tiss and Arey.) 



ridge known as the rhombic lip. From the portion of this ridge caudal to the 

 lateral recess develop the taenia of the fourth ventricle and the obex. At the 

 level of the recess the fibers of the acoustic nerve reach the dorsal edge of the 

 alar lamina, which, accordingly, undergoes development at this point into 

 vestibular and cochlear nuclei. More rostrally it undergoes an excessive devel- 



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