THE MEDULLA OBLONGATA. 



373 



In Pig. 236 this entire roof is represented as having been remoyed, 

 allowing free view into the fourth ventricle. Its floor is bounded below by 

 the diverging posterior columns, above by the superior cerebellar peduncles, 

 which converge toward the corpora quadrigemina. This gives it its peculiar 

 diamond shape. 



In this figure the view of the medulla posteriorly indicates the gradual 

 disappearance of the posterior columns as they ascend, and that in place of 

 them the inferior cerebellar peduncles, the restiform bodies (see below), 

 appear. The protuberance in the upper part of the posterior median column 

 is called the clava; it arises from the deposit of the nucleus funiculi gracilis. 



An anterior view of the medulla (Fig. 337) shows, first, the thick swell- 



Fig. 238. — Section through the oblongata at the level of the posterior hyp- 

 oglossal roots (schematic). Hinterstrdnye, Posterior columns. Einterliorn, 

 Posterior horn. Torder-Seitetihorii , Antero-lateral horn. CereJ). Bahn, Lateral 

 cerebellar tract. Aus Ruokenmo rk , From the spinal cord. Attn H. Str. Kernen, 

 From the nuclei of the posterior columns. Schleife, Fillet. 



ing of the pyramids, arising out of the cord. External to them appear the 

 olivary bodies, at the head of the lateral columns, as two large tumefactions. 

 A little higher up the large transverse fibers of the pons apply themselves 

 across in front of the pyramids. In the extension of the anterior radicular 

 groove upward, between the olive and the pyramid, arises the nervus 

 hypoglossus {XII) from the medulla. The nervus accessorius Willisii (XI) 

 arises from the cervical cord, and higher, from the medulla, external to 

 the olive, by numerous small bundles. Above, in the same groove ex- 



