XXXII] THE SPINAL BULB 253 



Dog. Sections 2 and 3. The bulbar root of the 5th nerve and its 

 nucleus are relatively larger than in man ; the sensory decussation 

 is less obvious ; the antero-lateral nucleus is formed earlier and is 

 probably present in (2); the- oblique fibres of the pyramid are better 

 marked off from the continuation of the anterior column (2) ; the 

 pyramid is relatively smaller (3). 



4. Section about 2 mm. above the lower end of the lower 

 olive and just below the 4th ventricle. 



The central grey substance is larger and stretches in a point 

 with the elongated central canal nearly to the dorsal surface, the 

 accessory nucleus of the funiculus cuneatus is larger and in 

 several bundles, the external arcuate fibres are throughout more 

 numerous, a thin bundle of them nearly covers up the funiculus 

 cuneatus ; the bulbar 5th is a half-moon shaped mass. 



Note : 



The raphe, a thin band in the median line below the central 

 canal, here chiefly composed of fibres running dorso-ventrally 

 and obliquely. 



The white reticular area on either side of the raphe, 

 composed almost entirely of nerve fibres, and the grey reticular 

 area laterally of the white, composed of nerve fibres intermixed 

 with grey substance (the distinction is more obvious in the next 

 section). .The dorsal part of the white reticular area is the 

 anterior column tract ; the ventral part is the fillet, here the 

 continuation of the fibres of the sensory decussation. 

 



The fillet between the accessory and lower olives is sometimes 

 called the inter- olivary tract. 



Ventrally and laterally in the central grey substance a group 

 of large angular cells, the nucleus of the 12th nerve (hypo- 

 glossal); bundles of fibres of the nerve may be seen at the 

 junction of the white and grey reticular areas and between the 

 olive and pyramid. 



Dorsally and laterally in the central grey substance, a some- 

 what oval group of moderate sized elongated cells, the dorsal 



