34 GRAY SUBSTANCE OF THE MEDULLA OBLONGATA 



pyramidal nucleus is not everywhere isolated, but, on the contrary, as will be seen 

 from my own figures (Figs. 21", 22", 23", 24", s), is in some places closely connected 

 with the lamina and in others separated from it, while in some cases it is divided 

 into three or four little groups, some of which, though doubtless connected more or 

 less with the pyramids, are stiU evidently offshoots from the olivary lamina. The 

 accessory olivary body of Stilling seems to be a sort of intermediate group between 

 the cells of the antero-lateral nucleus and the olivary lamina, and in sections from 

 the upper part of the medulla (Figs, 23", 24") it is replaced by the cells of the former 

 nucleus and by large multipolar cells lying in the same situation. 



As Ave ascend towards the pons, the hilus of the olivary bodies becomes succes- 

 sively more and more contracted, the folds of the lamina increasing somewhat in 

 depth, but diminishing rapidly in number, until, finally, the lamina is reduced to 

 much the same state as at its outset, becoming a closed coil of cells and fibres, which 

 soon entirely disappears, leaving only a few scattered cells to mark its situation in 

 the antero-lateral network which is now much encroached upon by the rapidly 

 increasing fibres %f the pons VaroUi. 



The cells of the olivary lamina are quite small, measuring aboutj-Jg g to -^ Jg^ of 

 an inch, agreeing very closely with Clarke's measurement (^ gVo — tsVo) ' t^^^^y are 

 very numerous and are quite uniform in size. My measurements of the average 

 thickness of the lamina vary much in different specimens, the smallest measure- 

 ment being about -g-^ ^ of an inch, and the largest -^^ of an inch ; in the same 

 medulla I have however foimd but very little variation, either in longitudinal or 

 transverse sections. 



Each olivary body is joined to its opposite fellow by a transverse commissure of 

 fibres decussating at the raphe, by means of which they are brought into very close 

 connection, as has already been pointed out by several authors. These commissural 

 fibres may be well seen in Figs. 25, 26, 27, and 28, and especially in Fig. 29, but 

 I have nowhere found such a strongly marked band without any intermingling of 

 longitudinal fibres, as is represented by Lenhossek,^ and I cannot fail to agree with 

 the criticism of Kolliker- on Lenhossek's description of the olivary commissure. 

 The fibres which serve to connect the olivaries, are for the most part as stated by 

 KoUiker, a direct continuation of the inner bundles of arciform fibres, which, as was 

 shown above, penetrate the olivary lamina at varying angles, a portion entering 

 cells, and the remainder forming a most intricate and complicated plexus with the 

 fibres derived from the cells of the lamina. Both of these sets of fibres, viz., those 

 entering cells and those passing among the cells, are, many of them at least, continued 

 forwards towards the raphe, forming a very beautiful network around the numerous 

 lono-itudinal bmidles which pass upAvards in the anterior part of the medulla on 

 each side of the median line. Some of these fibres turn upAvards, accompanying 

 the longitudinal bundles, but very many of them may be seen^to decussate at the 

 raphe, forming a commissural connection betAveen the opposite sides of the medulla. 

 At the same time, hoAvever, it must be borne in mind, that Avhile some of these 

 decussating fibres do undoubtedly originate in the cells of the olivary lamina and 



Neue Untersucbungen. Wien, 1859, pi. ii, fig. 2. ° Gewebelehre, 1862, 320. 



