. The anatomy of the central nervous system of man and of vertebrates in general. Neuroanatomy; Central Nervous System. 118 ANATOMY OF THE CENTEAL NEKVOUS SYSTEM. in the nuclei of the posterior cohimns, and in the gray matter of the spinal cord: Tractus tecto-spinales et tecto-bulbares. In adnlt animals the deep medullary layer of the midbrain may be best stiidied where it is best developed: , in birds or in fishes. The teleosts present the especial ad- vantage that the region in which the Stratum medullare prof, lies is rela- tively simple in structure; so that the tracing of the fibers i
. The anatomy of the central nervous system of man and of vertebrates in general. Neuroanatomy; Central Nervous System. 118 ANATOMY OF THE CENTEAL NEKVOUS SYSTEM. in the nuclei of the posterior cohimns, and in the gray matter of the spinal cord: Tractus tecto-spinales et tecto-bulbares. In adnlt animals the deep medullary layer of the midbrain may be best stiidied where it is best developed: , in birds or in fishes. The teleosts present the especial ad- vantage that the region in which the Stratum medullare prof, lies is rela- tively simple in structure; so that the tracing of the fibers is facilitated. If one becomes once familiar with the relations in teleosts he may find them readily again in any of the higher vertebrates. In Fig. 68 one may find several of the structures above mentioned. The tegmental decussation is not, however, to be readily found. In the enor- mous extension of the roof, which is found in the teleosts, these fibers have come into another position. They lie now directly upon the decussation which the lateral position of the meduUated stratum makes, and thus in-. Fig. 69.—Transverse section through the midbrain of a toad: Buf. cin. creases the commissura ansulata. In horizontal sections one may readily separate the two parts of the commissure (see Fig. 91). The fiber-system of the medullary stratum from the roof of the mid- brain fills a large part of the basal portion of that brain-segment, encircling and traversing it. Because of the great number of transverse fibers, the base of the midbrain has been called the Pars commissuralis. The roof of the midbrain gives origin to still another system from the same layer: viz., the fibers which, taken together, are much greater than parts mentioned, and which, throughout the whole roof region, pass in lateral direction from right to left or vice versa. Through these fibers there is formed in the median line the dorsal decussation of the midbrain. The whole structure is the Lamina commissuralis m
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