THE BULB. 591 



mlds % above which the place of the anterior columns of the spinal cord is 

 taken by two larger, more prominent columns, the pyramids of the bulb 

 (Py.), which are continued forward to the hind margins of the pons. On 

 the other side of, lateral to, each pyramid lies a projecting oval mass, the 

 olivary body or inferior olive (ol.) separating the pyramid from a column of 

 white matter, the restiform body (JR), which, occupying the lateral region of 

 the bulb, when traced backward appears to continue the line of the lateral 

 column of the cord, and when traced forward is seen to run up to the cere- 

 bellum as the inferior peduncle of that organ. On the posterior dorsal 

 aspect no such decussation is seen. The two posterior columns of the cord 

 diverge from each other, leaving between them a triangular space, the 

 calamus scriptorius, which is the hind part of the lozenge-shaped shallow 

 cavity of the fourth ventricle. As the cord passes into the bulb, the poste- 

 rior column, as a whole, grows broader, and the division into a median pos- 

 terior and an external posterior column becomes very obvious and distinct 

 by the appearance of a conspicuous furrow separating the two. At some 

 distance, however, in front of the point of divergence of the columns or 

 apex of the calamus scriptorius, the furrow becomes less marked, and it 

 eventually fades away. In its course the furrow takes such a line that the 

 median posterior column, forming the immediate lateral boundary of the 

 fourth ventricle, has the appearance of a strand broad behind but thinning 

 away in front, while the external posterior column, also broadening as it 

 advances forward, seems to be wedged in between the median posterior 

 column on its median edge and the restiform body on its lateral edge ; 

 hence the former is here called the fasciculus (or funiculus) gracilis (in. p.\ 

 and the latter the fasciculus (or funiculus) cuneatus (e. p.). Further forward 

 both columns seem to merge with each other and with fibres which curve 

 round to form part of the restiform body ; the relations, however, of these 

 two columns to each other and to the other parts of the bulb, as well as 

 the nature of the other several changes by which the cord is transformed 

 into the bulb, are disclosed by transverse vertical (dorso-ventral) sections, 

 to the study of which we must now turn. 



A section (Fig. 132, 1) taken at the hind margin of the decussation, at 

 which level the first cervical nerve takes origin, when compared with a sec- 

 tion of the cord at the level of the second cervical nerve (cf. Fig. 127, C 2 ), 

 shows that certain changes are already taking place in the gray matter. The 

 anterior horns are not much altered, but the posterior horns are, as it were, 

 pushed out laterally and dorsally so that the posterior columns, which as yet 

 retain their previous great depth, become very much broader than they are 

 lower down, encroaching, so to speak, on the lateral columns. At the same 

 time the substance of Rolando (. g.), forming the head or caput of the horn, 

 has enlarged into a more or less globular form, and lies near the surface of 

 the cord though separated from it by a compact tract of longitudinal fibres 

 ( V. a.}, which, as we shall see, belongs to the fifth cranial nerve. A con- 

 siderable development of the reticular formation (/. ret.) at the side of the 

 gray matter ventral to the posterior horn has also taken place, and this with 

 the shifting of the position of the posterior horn has driven the lateral horn 

 (/. h.) nearer to the anterior horn. From this lateral horn a root of the 

 eleventh spinal accessory cranial nerve (XL) may be seen taking origin. 

 Further, a great increase of gray matter round the central canal may also 

 be observed. 



These changes, however, are of degree only ; what seems to be an abso- 

 lutely new feature is the presence of bundles of fibres (Py. dec.) which start- 

 ing from the anterior column of one side cross over to and are apparently 

 lost in the gray matter of the neck of the anterior horn of the other side ; in 



