THE MEDULLA OBLONG ATA. 



695 



Restiform body. 



Clava. 



Cuneate tubercle. 



sation, through the medulla to its inner or mesial side. This decussation is usually 



spoken of as the decussation of the pyramids, but it must be borne in mind that it is 



only a portion of the fibres of the pyramid which 



decussate ; namely, those derived from the crossed 



pyramidal tract of the cord ; the outermost fibres, 



derived from the anterior column of the cord, 



do not decussate. Each pyramid enters the 



substance of the pons in one bundle, and may 



be traced through it, after breaking up into 



several smaller fasciculi, into the corresponding 



crus cerebri. 



The lateral column, in the lower part of the 

 medulla, is of the same width as the lateral 

 column of the cord, and appears on the surface 

 to be a direct continuation of it. As a matter 

 of fact it is only a part of the lateral column of 

 the spinal cord which is continued upward into 

 this column; for the crossed pyramidal tract 

 passes into the pyramid of the opposite side, 

 and the direct cerebellar tract of the lateral 

 column of the cord passes into the restiform 

 body. The rest of the lateral column of the 

 cord, that is to say, the antero-lateral ground 

 bundle and the antero-lateral cerebellar tract, 

 can be traced upward into this area. In the 

 upper part of the medulla, the lateral tract, 

 on account of the interpolation of the olivary 

 body, becomes almost concealed by this body. 



The olivary body is a prominent oval mass, 

 situated on the outer side of the pyramid, from 

 which it is separated by a slight groove, along 

 which the fibres of the hypoglossal nerve 

 emerge. It is separated externally from the 

 restiform body by a longitudinal, narrow band of fibres, prolonged upward from 

 the lateral tract, and by a groove, from which the glosso-pharyngeal, pneumo- 

 gastric, and spinal accessory nerves arise. It is equal in breadth to the pyramid ; 

 it is broader above than below, and is about half an inch in length, being separated 

 above from the pons Varolii by a slight depression, in which a band of arched 

 fibres is sometimes to be seen. Numerous white fibres (superficial arciform fibres) 

 are seen winding across the lower half of the pyramid and the olivary body to 

 enter the restiform body. 



The funiculus of Rolando is a longitudinal prominence on the outer side of the 

 lateral tract. It begins at the lower end of the medulla by a tapering extremity, 

 and has, apparently, no corresponding column in the cord. It gradually enlarges 

 as it ascends, and forms, at a level with the lower border of the olivary body, a 

 considerable prominence, known as the tubercle of Rolando. This is caused by 

 the substantia gelatinosa of Rolando of the cord gradually finding its way to the 

 surface, so as to form a prominence there. About half an inch below the pons the 

 funiculus of Rolando appears to blend with the funiculus cuneatus. In front, it is 

 separated from the lateral tract by a distinct groove, the continuation upward of 

 the postero-lateral groove of the cord ; behind, the separation from the funiculus 

 cuneatus is much less distinct. 



The funiculus cuneatus is the direct continuation upward of the postero-lateral 

 column (tract of Burdach) of the cord. It is situated between the funiculus of 

 Rolando and the funiculus gracilis. It enlarges as it ascends, and forms, opposite 

 the lower extremity of the fourth ventricle, a slight eminence or enlargement, the 



FIG. 370. Posterior surface of the me- 

 dulla oblongata. 



