Fig. 4.—Transverse section of both halves of the cord, cervical region. a, Fissure separating the anterior columns; b, fissure of the posterior.
Fig. 5.—Transverse section of the cord in the dorsal region.
Fig. 6.—Transverse section in the lumbar region.
Although the Medulla Spinalis is unquestionably continued as the Medulla Oblongata, the arrangement of its tissues here becomes gradually changed, and so complicated that it baffles the scalpel. Anatomists are, however, agreed on the one point of fundamental importance to us here—namely, that there is only a rearrangement, not a new tissue. Accepting the artificial division into two organs, we may say that their functions are different, inasmuch as they are different in their anatomical connections—they innervate different parts; but as nerve-centres they have one and the same property.
On its posterior surface the Medulla Oblongata opens as the fourth ventricle. It is then no longer a closed canal, but an expansion of the spinal canal, which is covered by the Cerebellum. On its anterior surface projects the pons varolii. [Figs. 7] and [8] represent these.
Fig. 7.—Back, or upper view of the Medulla Oblongata as it continues the Med. Spinalis. 1, Section of the thalami; 2, corpora quadrigemina (the two lower bodies are imperfectly represented in the engraving); 3, section of the crura cerebelli; 4, the fourth ventricle; 5, the restiform bodies; 6, the calamus scriptorius.