2 GRAY SUBSTANCE OF THE MEDULLA OBLONGATA. 



tufts may be seen arising from the gray substance ; these are the first indications of 

 the network of fibres and cells, which higher up is so very conspicuous, nearly fill- 

 ing the posterior pyramids, and separated from the restiibrm bodies by a distinct 

 sulcus (Figs. 1, 1", 2>). At the side of these little tufts a large and very distinct 

 eminence wUl be noticed, occupying the remainder of the posterior portion of the 

 cervix cornu, and projecting outwards into the restifbrm body, into which it sends 

 numerous fibres and cells. These two new bodies, which appear to fulfil a very 

 important part in" the organization of the medulla, Clarke has already named the 

 post-pyramidal and restiform tiuclei or ganglia. "They exist in all the mammalia.'" 

 The ca2nit cornu, meanwhile (Figs. 1, 2, 1", 2", &), has been pushed forwards, 

 and almost separated from the cervix by intervening network, imtil it nearly 

 reaches the surface of the postero-lateral columns, formmg the tuherculo cinereo or 

 gray tubercle of Rolando (h). The cervix contains many scattered cells of various 

 sizes, collected into several groups near the tufts which are the first indications of 

 the post-pyramidal and restiform nuclei. The caput contains only very small cells, 

 scattered about amcyig the longitudinal bundles which traverse it. Numerous 

 large cells are found among the fasciculi forming the fibrous network around the 

 lateral and antero-lateral gray substance, especially in that portion reaching from 

 the entrance of the spinal accessory along the lateral edge of the anterior cornu. 



The tractus intermedio-lateralis is well marked here, but as we ascend, only a few 

 large cells remain in the outer network, the majority being pushed inwards to form 

 the nucleus of the spinal accessory ; it is usually, however, quite possible to trace a 

 continuous line of cells from the entrance of the spinal accessory nearly to the cen- 

 tral canal. 



The anterior cornua are much diminished in size, and contain but few large cells 

 which are already partially collected in two small, round groups (Fig. 1", H), form- 

 ing the first indication of the great hypoglossal nuclei. » 



In the lateral columns near the border of external arciform fibres, a group of 

 large multipolar cells is found (Fig. I'*, B) which become more and more prom- 

 inent as we ascend, till the level of the vagus is reached, when it is broken up 

 into smaller groups. From its situation in the antero-lateral columns I propose to 

 call this group the anterolateral nucleus. It is penetrated by the fibres of the 

 arciform plexus, both external and internal, with which it is brought into very 

 close connection. 



(2.) A little higher up (Plates I, XIII, Figs. 2, 2") these changes in form are 

 still more marked; the decussation of the pyramids has ended. The pyramidal 

 columns which in the sheep are very small are now quite distinct ; and numerous 

 fibres run parallel to the axis of the medulla, forming with the arciform fibres which 

 decussate with them the raphe {R). The principal morphological change is the 

 appearance of the olivary bodies (0), which, though not particularly well marked 

 in the sheep, are stiU quite too distinct to be overlooked, as has been done by some 

 anatomists. They are composed of layers of small cells penetrated by the arciform 

 fibres; but I shall reserve the discussion of their more intimate structure for a 



' Medulla Oblongata. Philos. Trans. 1858, 240. 



