MEDULLA OBLONGATA. 391 



under a portion of the middle lobes of the cerebrum and of the 

 cerebellum. There is a longitudinal depression on its surface, 

 made by the basilar artery ; and there are also many transverse 

 streaks on it. 



The crura of the cerebellum, which runs into this substance, 

 are evidently continued from the arbor vita3 or medulla of the 

 cerebellum. 



The anterior edge of the cerebellum, part of which is in con- 

 tact with the pons Varolii, is remarkably prominent on each 

 side of it. These prominences are called the Vermes of the 

 cerebellum. 



The medulla oblongata is continued backwards from the pos- 

 terior side of the tuber ; and somewhat resembles a truncated 

 cone inverted. 



It lies on the cuneiform process of the occipital bone, and 

 extends to the foramen magnum. It is indented lengthwise, 

 both anteriorly and posteriorly, by fissures which are very 

 evident : it is composed of medullary matter externally, and 

 cineritious matter within. 



On each side of the anterior fissure, which is in view when 

 the brain is inverted, are two oblong convex bodies : those 

 which are next to the fissure are called the Corpora Pyrami- 

 dalia, and are the longest ; the two exterior are called Corpora 

 Olivaria, and are not so long. 



The third pair of nerves come from between the crura of the 

 cerebrum, and pass forward, diverging from each other. They 

 proceed by the cavernous sinus, and, after penetrating the dura 

 mater, go out of the cranium at the foramen lacerum. 



The fourth pair, the smallest nerves of the brain, resemble 

 sewing thread in their size and appearance. They come out 

 between the cerebellum and pons Varolii, but can be traced 

 backwards as far as the testes. They proceed forwards by the 

 sides of the pons Varolii, and after penetrating the dura mater 

 near the posterior clinoid apophysis, pass through the foramen 

 lacerum to the trochlearis muscles of the eye. 



The fifth pair } the largest of the brain, arise from the crura 

 of the cerebellum, where they unite with the pons varolii : they 



