this order is reversed. The fibres of the spinal cord, before entering
this portion of the brain, decussate, those from the right side crossing
to the left, and those from the left crossing to the right side. By some
authors this crossing of the sensory and motor filaments has been
supposed to take place near the medulla oblongata. Dr. Brown-Sequard
shows, however, that it takes place at every part of the spinal cord.
The medulla oblongata is traversed by a longitudinal fissure, continuous
with that of the spinal cord. Each of the lateral columns thus formed
are subdivided into sections, termed respectively the _Corpora
Pyramidalia_, the _Corpora Olivaria_, the _Corpora Restiformia_ and the
_Posterior Pyramids_.

The _Corpora Pyramidalia_ (see 1, 1, Fig. 58) are two small medullary
eminences or cords, situated at the posterior surface of the medulla
oblongata; approaching the Pons Varolii these become larger and rounded.

The _Corpora Olivaria_ (3, 3, Fig. 58) are two elliptical prominences,
placed exterior to the corpora pyramidalia. By some physiologists these
bodies are considered as the nuclei, or vital points, of the medulla
oblongata. Being closely connected with the nerves of special sensation,
Dr. Solly supposed that they presided over the movements of the larynx.

[Illustration: Fig. 58.]

[Illustration: Fig. 59.]

The _Corpora Restiformia_ (5, 5, Fig. 59) are lateral and posterior
rounded projections of whitish medulla, which pass upward to the
cerebellum and form the _crura cerebelli_, so called because they
resemble a leg. The filaments of the pneumogastric nerve originate in