568 MEDULLA OBLONGATA. 



part, and about six lines thick. Below, it is continuous insensi- 

 bly with the spinal marrow ; above it terminates in, or rather 

 passes through the pons varolii, (fig. 224,) by means of which it 

 is continuous with the cerebrum ; and on its back part through 

 the corpora restiformia, it is continuous with the cerebellum. 

 The anterior median fissure of the medulla spinalis is con- 

 tinued up over the medulla oblongata ; it may be traced as a 

 superficial groove over the pons varolii and is seen terminating 

 in the fissure between the crura cerebri. 



The posterior median fissure extends up on the back part of 

 the medulla oblongata, to a cavity called the fourth ventricle, 

 where the back part of the medulla oblongata seems to open 

 and branch off towards the cerebellum. These two fissures 

 divide the medulla oblongata into two lateral halves, like the 

 divisions of the spinal marrow. On each of these divisions we 

 observe three elevations. One called the corpus pyramidale (B. 

 fig. 224), from its triangular shape, which is broader above than 

 below, and bounds the anterior median fissure ; one called the 

 corpus restiforme, from its rounded shape, m, that forms the side 

 of the posterior median fissure as well as part of that of the 

 fourth ventricle, where it diverges from its fellow to go to the 

 cerebellum. Between the two, upon each side, is seen an ob- 

 long elevation, called the corpus olivare, c c, which is situated 

 a little obliquely from without inwards, and from above down- 

 wards. These three bodies do not, however, occupy the whole 

 surface of the medulla oblongata ; between the corpus olivare 

 and the corpus restiforme, an unelevated band of fibres is seen 

 passing up called the corpus innominatum by Cruveilhier,* and 

 which was first particularly pointed out by Sir C. Bell, as the 

 lateral column.^ 



In the account of the spinal marrow, it has been observed 

 (page 556,) that the anterior and posterior roots of the spinal 

 nerves, have been proved unquestionably to be endowed with 



* Sir C. Bell's division of each half into three columns, is no longer con- 

 sidered tenable. 



f These parts have had the name of posterior pyramids applied to them by 

 Rolando and Ollivier. The same term has been applied by others to the corpus 

 restiforme. 



