946 THE GREY MATTER OF THE BULB. [BOOK in. 



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

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

 distinguished (Fig. 109, 6, ol. e) by the name outer accessory nucleus 

 from the above mentioned inner accessory nucleus. It will be 

 observed in these transverse sections that the inner accessory 

 nucleus is separated from the olivary nucleus by a bundle of 

 white fibres (Fig. 109, 4, 5, 6, Xil) which, running ventrally from 

 the grey matter in the dorsal region, comes to the surface between 

 the anterior pyramids and the olivary body. This is the hypo- 

 glossal or twelfth cranial nerve. 



On the surface of the anterior pyramid itself is seen on each 

 side a small mass of grey matter (Fig. 109, 5, 6, n. a.), which since 

 it appears to be connected with a system of superficial transverse 

 fibres, which we shall describe directly as the external arcuate 

 fibres (Fig. 109, 3, 4, 5, 6, f. 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 grey matter 

 is seen in sections as a rounded mass of irregular form placed 

 lateral to the reticular formation (Fig. 109, 4, 5, 6, a. I. n). This, 

 which at its first appearance seems to be budded off from the 

 general mass of grey matter (Fig. 109, 3, a. I. n) and which is 

 probably a detached portion of the base of the anterior horn or of 

 the lateral region of the grey matter, is called the lateral or antero- 

 lateral nucleus. 



Hence, besides the diffuse reticular formation, this ventral 

 part of the bulb contains more sharply defined collections of 

 grey matter in the olivary nucleus, and the other bodies just 

 mentioned. 



610. We must now turn to the dorsal part of the bulb. 

 Here in the first place we must distinguish between the portions 

 of grey matter which are more immediately connected with the 

 cranial nerves taking origin from this part of the bulb, and the 

 portions which have no such obvious connection. In the spinal 

 cord, the anterior horns supply, as we have seen, the origins of the 

 successive anterior motor nerves; but in the transformation of 

 the cord into the bulb the anterior horns have been broken up 

 or displaced ; and the parts of the anterior horns, serving as the 

 nuclei of origin for motor nerves, have been translated from the 

 ventral to the more dorsal regions. Hence, it is in the more 

 dorsal part of the grey matter that we have to seek for the nuclei 

 of origin not only of afferent but also of motor cranial nerves. 

 It will be convenient to consider all these nuclei of origin of 

 cranial nerves by themselves, and we may here confine ourselves 

 to the grey matter of other nature. We may however say that 

 these nuclei from that of the third nerve backwards are more or 

 less closely associated with the grey matter immediately sur- 

 rounding the central canal. This central grey matter, in the 

 narrow sense of the term, is marked out somewhat low down 



