MEDULLA OBLONGATA. 401 



sional exceptions, when the injury is felt on the same 

 side. 



The Corpora pyramidalia } or anterior pyramids, are sit- 

 uated upon either side of the median fissure, extending the 

 whole length of the medulla oblongata, and represent two 

 white, convex, and narrow bands, placed side by side. 

 They each arise at the point of decussation, as above stated, 

 by two sets of fibres the one from the opposite anterior 

 column of the spinal marrow the other from the same 

 side with itself. As they enter the pons they become con- 

 stricted, and can be traced through it to the crura cerebri, 

 forming their outer and anterior portions. 



Corpora Olivaria, so named from their resemblance to an 

 olive, are situated to the outside of the corpora pyramid- 

 alia, are shorter, and more convex than the pyramids, and 

 separated from them and the restiform bodies by a groove. 

 They consist of two beautiful white bodies, which proceed 

 from the antero lateral column of the spinal marrow, and 

 continue through the central portion of the medulla ob- 

 longata, extending to its posterior surface, forming the 

 floor of the fourth ventricle. These bodies can be traced as- 

 cending behind the corpora pyramidalia, through the pong, 

 to the posterior portions of the crura cerebri, and thence to 

 the tubercula quadrigemina, and optic tlialami. Some curved 

 fibres, termed arciform, pass over the corpora olivaria from 

 the pyramids to the corpora restiformia ; they vary in num- 

 ber and size, and are regarded as commissural between the 

 bodies with which they are connected. 



The olivary bodies are found to exist only in man and 

 the quadrumana. On being divided, a quantity of gray 

 matter is seen, called the olivary ganglion. 



The Corpora Eestiformia (restis, a rope) are situated 

 upon the side and posterior part of the medulla oblongata, 

 separated from the corpora olivaria by a groove, and from 

 each other superiorly by the fourth ventricle, and inferi- 

 orly by the posterior median fissure. They are continuous 

 with the posterior and part of the antero lateral columns 

 of the spinal cord, and are traced ascending and diverging 

 26 



