426 MEDULLA OBLONGATA. 



across the upper part of the medulla oblongata ; and, contracting on 

 each side into a thick rounded cord, enters the substance of the cere- 

 bellum under the name of eras cerebelli. There is a groove along its 

 middle which lodges the basilar artery. The pons Varolii is the com- 

 missure of the cerebellum, and associates the two lateral lobes in their 

 common function. Resting upon the pons, near its posterior border, 

 is the sixth pair of nerves. On the anterior border of the cms cere- 

 belli, at each side, is the thick bundle of filaments belonging to the 

 fifth nerve, and, lying on its posterior border, the seventh pair of 

 nerves. The upper surface of the pons forms a part of the floor of the 

 fourth ventricle. 



MEDULLA OBLONGATA. 



The medulla oblongata (bulbus rhachidicus), is the upper enlarged 

 portion of the spinal cord. It is somewhat conical in shape, and a 

 little more than an inch in length, extending from the pons Varolii to 

 a point corresponding with the upper border of the atlas. On the 

 middle line, in front and behind, the medulla oblongata is marked by 

 two vertical fissures, the fissura longitudinalis anterior and posterior, 

 which divide it superficially into two symmetrical lateral cords or co- 

 lumns ; whilst each lateral column is subdivided by minor grooves into 

 three smaller cords, namely, the corpora pyramidalia, corpora olivaria, 

 and corpora restiformia. 



The Corpora pyramidalia are two narrow convex cords, tapering 

 slightly from above downwards, and situated one on either side of the 

 sulcus longitudinalis anterior. At about an inch below the pons the 

 corpora pyramidalia communicate very freely across the sulcus by a 

 decussation of their fibres, and at their point of entrance into the pons 

 they are constricted into round cords. The fissura longitudinalis is 

 somewhat enlarged by this constriction, and the enlarged space has re- 

 ceived the name of foramen coecum of the medulla oblongata. 



The Corpora olivaria (named from some resemblance to the shape 

 of an olive), are two oblong, oval-shaped, convex bodies, of about the 

 same breadth with the corpora pyramidalia, about half an inch in 

 length, and somewhat larger above than below. The corpus olivare is 

 situated immediately external to the corpus pyraraidale, from which, 

 and from the corpus restifonne, it is separated by a well-marked groove. 

 In this groove some longitudinal fibres are seen which enclose the 

 base of the corpus olivare, and have been named funiculi siliquce, those 

 which lie to its inner side being the funiculus internus, and 

 those to its outer side the funiculus externus. Besides these 

 there are other fibres which cross the corpus olivare obliquely, 



of nerves. 18. The seventh pair of nerves consisting of the auditory and facial. 

 19- The corpora pyramidalia of the medulla oblongata ; the corpus olivare and 

 part of the corpus restiforme are seen at each side. Just below the numeral is 

 the decussation of the fibres of the corpora pyramidalia. 20. The eighth pair 

 of nerves. 21. The ninth or hypoglossal nerve. 22. The anterior root of the 

 first cervical spinal nerve. 



