Abstract
(1.) Galen believed that the
medulla spinalis
commences as high up as the lower border of the
pons Varolii
. This, like nearly every other, opinion of the Greek anatomist was adopted by all his successors until the time of Sylvius and Vesalius. Sylvius traced the origin of the spinal chord from the whole base of the brain
1
; Vesalius, only from the
corpora quadrigemina
2
. Columbus
3
, Varolius
4
, Spigelius
5
, Laurentius
6
, Riolanus
7
, Highmore
8
, described it as arising by two roots,—one large, from the entire base of the brain; the other small, from the cerebellum. But Piccolhomini introduced a better description of these parts, by restricting the term “ medulla
spinalis
” to the contents of the spinal column; while to the whole
intra-cranial
prolongation along the base of the brain, he applied the term “ medulla
oblongata
”
9
, which has been retained to the present day, though many anatomists have differed with regard to the number of parts it has been supposed to comprehend. According to Willis
10
, it includes the
whole base
of the brain, from the
corpora striata
—which he called “medullæ oblongatæ apices"—to the
foramen magnum
. The same view was adopted by Vieussens
11
, Winslow
12
, and others; while Rolando
13
employed the term in a more restricted sense ; and Ridley
14
, who did the same, substituted for it the term “isthmus,” and Chaussier
15
that of “mesocephale,” which included the
pons, tubercula quadrigemina
, with the
superior peduncles of the cerebellum
, and not the pons
only
, as sometimes stated. Flourens
16
, again, on the ground of his experimental inquiries,—which led him to conclude that the seat of
excitability
begins or ends with the
corpora quadrigemina
,—limits the
medulla oblongata
between these bodies and the eighth pair of nerves. In this country the
medulla oblongata
is generally understood to extend from near the points of the
anterior pyramids
to the lower border of the
pons
, and as such it is described in this memoir. (2.) It is well known that in the
spinal chord
the columns of white and grey substance are parallel to each other, and preserve the same relative position throughout their entire course; but in the
medulla oblongata
these parts not only assume a different arrangement, by becoming more or less blended with each other and with new structures, but frequently pursue a curvilinear direction in different planes inclined at varying angles. It is evident, therefore, that transverse and longitudinal sections, however transparent they may be made, must be insufficient, when employed alone, to complete the examination of so intricate a structure. For this reason, after having made myself thoroughly acquainted with the microscopical anatomy of these parts, and traced their relations and connexions, as far as possible, by my own method of preparation, which I find superior to any other that I have seen of the same kind, I then employed, in conjunction with it, the method of Reil; so that when necessary, the structure revealed at different stages of the dissection was compared with transparent sections through the same parts. Great assistance was also obtained by making, simply for my own use, as I dissected through the depth of a part, a multitude of sketches, which were placed side by side and carefully examined in succession: the plan is tedious and demands patience, but car be confidently recommended to anatomists as a valuable expedient for ascertaining the arrangements of a complicated and intricate structure of which the parts are so continually changing their course and relative position, in varying planes, that in the dissection each must necessarily be destroyed whilst seeking its relation to others.
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