Anatomy of M Brain. 553 



composed keep right on, however, into the cranium without break, so 

 that this limit at the great foramen is purely artificial. NevertheleHB, 

 soon after its entrance into the cranium, the body of the cord under- 

 goes modifications and new arrangement of parts, which justifies a 

 change in its name, and it is called the medulla oblongata. The front, 

 or anterior, part of the medulla oblongata rests upon the base or front 

 part of the occipital bone, which forms part of the base of the skull 

 Like the spinal cord, the medulla oblongata is divided into lateral halves 

 by a front and a dorsal groove, which correspond with, and are continu- 

 ations of the front and dorsal grooves of the cord. There are, conse- 

 quently, parts corresponding with the anterior, posterior and lateral col- 

 umns of the spinal cord, to which, however, new names are given. On 

 the anterior side of the medulla oblongata, and about midway of its 

 length, a large proportion of the nerve fibres of the column on the left 

 of the anterior groove or fissure, cross over the groove to the right side, 

 and those on the right cross to the left. (Fig. 266.) These anterior 

 <*>lumns are called the anterior pyramids, and this crossing of fibres is 

 the decussation of the anterior pyramids. The fibres of the pyramids 

 spread out as they go forward, so that the base of the pyramid is toward 

 the head end of the body. On each side of the anterior pyramids is an 

 ovoid eminence called, from its shape, the olive or olivary body. Seen 

 from the posterior side, the posterior columns of the medulla oblongata 

 appear to subdivide, the fibres on each side next the fissure forming a 

 distinct bundle, which, spreading out towards the forward end, become 

 the posterior pyramids. What is left of these posterior columns, to- 

 gether with the fibres of the lateral columns, constitute what are called 

 the restif orm bodies ( corpora restif orme ). which occupy the sides and 

 posterior parts of the medulla oblongata, between the posterior pyra- 

 mids and the olivary bodies. There are some fibres from the anterior 

 pyramids which pass around the inferior or hind ends of the olivary 

 bodies toward the restiform bodies, and accompany them forward toward 

 the cerebellum. These are called arcif orm fibres. (Fig. 267.) There 

 are other arciform fibres which leave the olivary bodies themselves and 

 make for the same destination. The functions of the different parts of 

 the medulla oblongata correspond largely with the functions of the cor- 

 responding parts of the spinal cord with which they communicate. The 

 -posterior pyramids and the restiform bodies, being chiefly derived from 

 the posterior half of the spinal cord, are chiefly sensory as it is, while 

 the anterior pyramids and the fibres of the olivary bodies, derived mostly 

 from anterior half of the spinal cord, are chiefly motor. These charac- 

 ters follow the fibres through the medulla into the ganglia beyond it, as 

 will be seen. 



There is a body of gray vesicular or brain matter connected with each 



