METENCEPHALON. 421 



and 80). It is not well formed until near birth and is produced 

 almost wholly by the enormous growth of the superior and the 

 inferior semilunar lobules which are so characteristic of the human 

 cerebellum (Cunningham). 



The cerebellar lobules are subdivided into gyri by intralobular 

 sulci which develop in the later months of pregnancy and the early 

 months of extrauterine life. There are two, called the midgra- 

 cile and postgracile sulci, which Bradley says are found only in 

 man and the anthropoid apes. 



Cortex and Ganglia. Little is known of the particular order 

 and manner of development in either the cortex or ganglia of the 

 cerebellum. As to the cortex, it consists in general, (i) of the 

 multiplication and development of the cells in the mantle layer, 

 some of whose processes descend to the cerebellar ganglia and 

 Deiters's nucleus, and, (2) of the formation of contacts with in- 

 growing fibers from pons, medulla and spinal cord. 



Corpus Restiforme of Cerebellum. Fibers from the cerebellar 

 cortex descending to the medulla, and ascending fibers from the 

 cord and medulla in their course to the cerebellar cortex, give 

 rise to the corpus restiforme in the third month. Fibers from 

 the nucleus pontis and nucleus fastigii form the brachium pontis 

 a month later and in the fifth month the brachium conjunctivum 

 is produced by fibers from the nucleus dentatus. 



Pons (Figs. 118, II, I, 121 and 122). The pons develops sim- 

 ultaneously with the cerebellum. The ventral zone of the met- 

 encephalon thickens greatly. The neuroblasts formed therein 

 constitute the nuclei of the pons ( ?) and of the reticular formation, 

 and the motor nuclei for the fifth, sixth and seventh pairs of cere- 

 bral nerves; the dorsal lamina in the lateral wall of the meten- 

 cephalon, produces the neuroblasts which form the superior olivary 

 nucleus and the superior part of the terminal nucleus of the trigem- 

 inal and of the acustic nerve. From the nucleus pontis axones 

 ascend through the lateral walls of the metencephalon to the cere- 

 bellum. They form most of the brachia pontis. At the same 

 time, about the fourth month, the motor tracts composing the 

 basis pedunculi grow downward into the ventral portion of the 

 pons and the fronfo- pontal, temporo-pontal and intermediate tracts 



