. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. INTERA'AL ANATOMY. 87 of them runs beneath the outer surface of the oral hood and, by the occurrence of frequent anastomoses, forms a coarse network known as the outer plexus, while the other set lies beneath the inner surface of the oral hood and gives rise to the inner plexus. The latter was discovered by FuSARi in 1889. The two plexuses are distinct from. Fig. 43.—Transverse section through the spinal cord in the middle region of the body. (After ROHUE.) a. Giant fibre proceeding from the giant ganglion-c
. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. INTERA'AL ANATOMY. 87 of them runs beneath the outer surface of the oral hood and, by the occurrence of frequent anastomoses, forms a coarse network known as the outer plexus, while the other set lies beneath the inner surface of the oral hood and gives rise to the inner plexus. The latter was discovered by FuSARi in 1889. The two plexuses are distinct from. Fig. 43.—Transverse section through the spinal cord in the middle region of the body. (After ROHUE.) a. Giant fibre proceeding from the giant ganglion-cell A (see below), Cen- tral canal, g. f^. Giant nerve-fibres, which traverse the spinal cord from before back\vards. Giant fibres, which traverse the spinal cord from behind for- wards, Muscle-plates, Motor nerve-fibres, n. f. Longitudinal ner\'e- fibres cut across, Supporting fibres, sh. Sheath of nerve-cord (— du7-a viater; \Ri). one another, except in so far as their component nerves have a common origin from the dorsal roots (Fig. 42), The outer plexus is continued up into the individual cirri, while the inner plexus appears to stop short at the base of the cirri. It has recently been discovered by van. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Willey, Arthur, 1867-. New York, London, Macmillan
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