. Cunningham's Text-book of anatomy. Anatomy. THE SPIXAL MEDULLA. 517 excrescences—the cerebral hemispheres—are budded off from it; and they become the dominant part of the nervous system (Fig. 458). Each hemisphere is formed, however, from a relatively small part of the lateral wall of the prosencephalon, the rest of which goes to form the optic diverticula, the thalamus, and the hypothalamus, among other structures. The cerebral hemisphere is at first pre-eminently olfactory in function, the nerves of smell being inserted directly into it. But impressions of the associated sense of taste mak
. Cunningham's Text-book of anatomy. Anatomy. THE SPIXAL MEDULLA. 517 excrescences—the cerebral hemispheres—are budded off from it; and they become the dominant part of the nervous system (Fig. 458). Each hemisphere is formed, however, from a relatively small part of the lateral wall of the prosencephalon, the rest of which goes to form the optic diverticula, the thalamus, and the hypothalamus, among other structures. The cerebral hemisphere is at first pre-eminently olfactory in function, the nerves of smell being inserted directly into it. But impressions of the associated sense of taste make their way into the cerebral hemisphere in the most primitive vertebrates: the gustatory nerves are inserted into the medulla oblongata, but fibre-paths are laid down to establish connexions with the hypothalamus, which in turn emits fibres to the cerebral hemisphere (Fig. 454). The thalamus is a greatly swollen part of the prosencephalic wall adjoining the mesencephalon. Its main part receives sensory impressions brought up from the spinal medulla and the terminal nuclei of the sensory cerebral nerves and transmits them to the cerebral hemisphere. Its caudal portion becomes specialised as a special receptive nucleus for visual and acoustic impressions for transmission to the cerebral hemisphere. It is called the metathalamus or corpora geniculata. Thus the cerebral hemi- sphere from being essentially a receptive organ for smell impressions ultimately becomes the terminus of all the sensory paths, and the structure that is concerned with the consciousness of all kinds of sensations. It also controls the voluntary movements of one-half of the body and emits a great strand of fibres—pedunculus cerebri—to establish relations with the cerebellum and all the motor nuclei on the other side of the encephalon and spinal medulla (Fig. 454, p. 513). MEDULLA SPINALIS. The spinal medulla is that part of the central nervous occupies the upper two-thirds of the vertebral canal. It i
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