84 ANATOMY OF THE HEAD AND NECK. 



the anterior ceasing at the pous Yarolii in a dilated pa 

 called the foramen caecum; the posterior is prolonged in 

 the floor of the fourth ventricle. Each half of the medulla 

 made up from the three lateral divisions of the spinal co 

 indications of which still exist, though they are somewh 

 differently arranged and changed in form. That porti 

 nearest the longitudinal fissure in front, is called the an 

 rior pyramid or corpus pyramidale ; at about an inch belo 

 the pons Varolii the pyramids of the two sides communica 

 across the anterior longitudinal fissure by what is called 

 decussation of their fibres. The anterior pyramids are t 

 continuation upward of the anterior columns of the spin 

 cord. Next the anterior pyramids comes the corpus oliva 

 This is an oval projection, separated by a groove on ea 

 side from the anterior pyramids in front, and the restifor 

 body behind ; its upper end is the most prominent, and d 

 n^t quite reach the pons Yarolii ; its lower end is characte 

 ized by some transverse fibres arching over its surface, whi 

 are called arciform fibres. That part of the medulla belo 

 the olivary body is continuous with the lateral column 

 the spinal cord, and is here sometimes called the later 

 tract ; its fibres are continued upward, much diminished 

 size, between the olivary and restiform bodies. On eac 

 side of the posterior longitudinal fissure is the corpus resti- 

 forme. This is the largest prominence of the medulla, and 

 by its lateral projection gives width to its upper part. The 

 posterior pyramids are placed on each side of the posteri 

 longitudinal fissure, lower down than the restiform bodi 

 and are the continuation upward of the posterior colum 

 of the spinal cord; at the lower part of the medulla th 

 diverge and become blended with the restiform bodies. 



The PONS YAROLII, or, as it is sometimes called, t 

 TUBER ANNULARE, is situated above the medulla oblonga 

 and between the hemispheres of the cerebellum ; it is of 

 square shape, the anterior border arching over the crura 

 cerebri, and theposterior over the medulla oblongata. Th 

 superficial fibres of the pons Yarolii aflt transverse, an 

 collect together on each side to form the crura cerebell 

 the deep fibres are longitudinal, and are prolonged upw 

 from the medulla. The crura cerebri are large stalk-like 

 bodies emerging from the anterior border of the pons Yarolii 

 and dipping into each lateral hemisphere of the cerebrum; 

 as they enter the hemispheres they are crossed transversely 

 by the optic tract. 



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