STRUCTURE OF THE MEDULLA OBLONGATA. 609 



lively small. In Fig. 215 the gray substance is seen to have relatively in- 

 creased in size, but to have become somewhat broken up. On each side of 

 the posterior median fissure a remarkable longitudinal column (6), contain- 

 ing gray matter in its interior, termed the " pyramidal column," is begin- 

 ning to appear; a second swelling, situated on the Cervix a little more 

 externally to that just mentioned, indicates the commencing appearance 

 of the restiform nucleus; still more externally, the Caput Coruu maybe 

 seen to be detached and thrown aside from the rest as a distinct mass, 

 which is traversed successively by the vagus and glosso-pharyngeal nerves, 

 and then becomes the principal nucleus of the sensory root of the fifth pair. 

 The decussation of fibres proceeding from the deeper part of the lateral 

 column (between p and a, Fig. 214) to form the anterior columns is also 

 here well seen, and the central gray substance has reassumed a triangular 

 form. In the next section (Fig. 216), made about ^ of an inch below the 

 olivary bodies, the gray matter of the posterior pyramids (6) on either side 

 of the posterior median fissure, is seen to have considerably increased in 

 size ; the slight swelling at the base of the Cervix is also now much larger, 

 and has become the gray nucleus of the restiform bodies (o), whilst what 

 was the Caput Cornu is pushed still further forwards, 

 and forms a great mass of gray matter at the side of 

 the cord known as the Gray Tubercle of Rolando 

 (e, Figs. 217, 218). The commissural direction and 

 arrangement of the fibres of the anterior pyramids 

 are also still apparent. They come principally from 

 the central gray substance, and scarcely at all from 

 the lateral columns. On making a section just below 

 the olivary bodies (Fig. 217), the gray matter is 

 found to occupy almost the whole of the posterior 

 pyramids (6), and a large portion of the restiform 

 bodies (o), whilst a most delicate and complex system 

 of interlacing fibres surrounds the central canal, section immediately below 

 The gray tubercle of Rolando having increased in Olivary bodies, 



size and reached the surface of the Medulla, appears 



as a dark streak (t, c, Fig. 212; ; the portion of the anterior column which 

 does not decussate has been left white on the right side of this drawing. 

 Two minute dark spots may be noticed near the bottom of the posterior 

 fissure; these are imbedded in the mass of cells forming the chief gangli- 

 onic centres of the spinal accessory nerve, though other and extremely fine 

 rootlets belonging to these nerves may be traced arising from the lateral 

 gray substance and base of the anterior cornu of the spinal cord or tractus 

 intermedio-lateralis, and issuing with the posterior roots of the Spinal nerves 

 as low down as the sixth or seventh cervical vertebra. Fig. 218 is taken 

 from a section made through the lower part of the Olivary body. The 

 posterior pyramids (6) still contain much gray matter, and the restiform 

 nucleus and gray tubercle of Rolando are strongly defined. The small 

 central canal has become closely approximated to the bottom of the poste- 

 rior median fissure, and on either side of it are the gangl ionic masses from 

 which the spinal accessory nerve takes its origin, whilst immediately in front 

 of it are two dark spots containing large multipolar cells indicating the 

 ganglia of origin of the hypoglossal nerve, other fibres of which last, like 

 those of the spinal accessory nerve, may be traced downwards, and arise from 

 the upper remains of the anterior coruu, whilst a few of the superior fibres 

 cross the raphe. Anteriorly the windings of the corpus dentatum or olivary 

 nucleus are visible, with a remarkable set of ganglionic cells indicated by 



