596 THE BKAIN. 



nearly all the way along the cord the gray matter of the neck of the poste- 

 rior horn is similarly broken up by bundles of fibres into what we there called 

 the reticular formation (Figs. 121, 122, r.f. p. and r.f. L) ; and this area in 

 the bulb though it possesses characters of its own is also called the reticular 

 formation, in the more lateral portion of this formation, the network is 

 more open and irregular, the fibres are finer, and the nerve-cells are more 

 abundant than in the median portion where the nerve-cells, except in the 

 immediate neighborhood of the raphe, are less numerous or even absent, and 

 the fibres are coarser. These two parts are sometimes distinguished as the 

 outer or lateral and the inner or median formation. In the middle line the 

 fibres distinctly interlace and decussate in an oblique manner, some running 

 nearly vertically in the dorso-ventral plane, thus constituting, as we have 

 said, a thick raphe, which, however, at its edges gradually mergesin to the 

 more open network. 



522. Within the area, bounded by the pyramids ventrally, the ex- 

 panded gray matter dorsally, the raphe in the middle line, and the white 

 matter laterally, certain distinct compact masses of gray matter make their 

 appearance, as we pass upward toward the pons. 



One of the most important of these gives rise to the olivary body, or in- 

 ferior olive, which, as we have seen, projects as an oval mass (Fig. 131, ol.) 

 on each side of the pyramids, reaching from a level which is somewhat 

 higher up than the lower limit of the pyramids, almost but not quite to the 

 pons. The olivary body, as a whole, consists partly of white matter, that is, of 

 fibres, and partly of gray matter, sometimes called the olivary nucleus. This 

 latter is disposed in the form of a hollow flask or curved bowl, with deeply 

 folded or plaited walls, having a wide open mouth directed inward toward 

 the middle line, and forward toward the pons (Fig. 132, 4, 5, 6, ol.*). The 

 flask is filled within by white matter, and covered up on its outside with 

 white matter as well as traversed by fibres. The gray matter thus forming 

 this flask-shaped nucleus consists of small rounded nerve-cells, lying in a 

 bed of tissue which is partly ordinary neuroglia, and partly a fine nervous 

 network. 



Lying to the median side of the olivary body, immediately dorsal to the 

 anterior pyramid is another small mass of gray matter, in the form of a disc, 

 appearing in transverse sections as a thick bent rod, in some sections consist- 

 ing of two parts (Fig. 132, 4, ol. a.). This is the accessory olivary nucleus. A 

 very similar body lies dorsal to the olivary nucleus, in the lateral reticular 

 formation ; this is also called an accessory olivary nucleus, being distinguished 

 (Fig. 132, 6, ol. e.) by the name outer accessory nucleus from the above-men- 

 tioned inner accessory nucleus. It will be observed in these transverse sec- 

 tions that the inner accessory nucleus is separated from the olivary nucleus 

 by a bundle of white fibres (Fig. 132, 4, 5, 6, XII.) which, running ventrally 

 from the gray matter in the dorsal region, comes to the surface between the 

 anterior pyramids and the olivary body. This is the hypoglossal or twelfth 

 cranial nerve. 



On the surface of the anterior pyramid itself is seen on each side a small 

 mass of gray matter (Fig. 132, 5, 6, n. a.), which since it appears to be con- 

 nected with a system of superficial transverse fibres, which we shall describe 

 directly as the external arcuate fibres (Fig. 132, 3, 4, 5, 6,/. a. e.), is called 

 the arcuate nucleus. It seems to belong to the same group as the accessory 

 olives. 



Lastly, a small somewhat diffuse collection of gray matter is seen in sec- 

 tions as a rounded mass of irregular form placed laterally to the reticular 

 formation (Fig. 132, 4, 5, 6, a. I. ?i.). This, which at its first appearance 

 seems to be budded off from the general mass of gray matter (Fig. 132, 3, 



