. Text book of zoology. Zoology. 376 Vertehrutu. another, as in the Siluroids, where the bases of well-developed rays may play against the subjacent bones. The hearty which is situated anteriorly (see Fig. 285 A), is usually almost bilaterally symmetrical. In Selachii, G-anoidei, and Dipnoi, it consists of a large thin-walled auricle; of a ventricle lying ventral to this, with thick walls of a spongy nature, owing to the numerous offsets passing into them from the small cavity; and lastly, of a tubular conus arteriosus, from the anterior end of which the trunk of the branchial arteries arises,
. Text book of zoology. Zoology. 376 Vertehrutu. another, as in the Siluroids, where the bases of well-developed rays may play against the subjacent bones. The hearty which is situated anteriorly (see Fig. 285 A), is usually almost bilaterally symmetrical. In Selachii, G-anoidei, and Dipnoi, it consists of a large thin-walled auricle; of a ventricle lying ventral to this, with thick walls of a spongy nature, owing to the numerous offsets passing into them from the small cavity; and lastly, of a tubular conus arteriosus, from the anterior end of which the trunk of the branchial arteries arises, and in which several rows of membranous watch-pocket valves are. Fig. 310. Diagramraatio longitudinal section of the heart of different Fish. A of a Pish with well-developed conns, B of Amia, 0 of a Teleostean ; in B and 0 the auricle is cut away. a auricle, b bulbus arteriosus, which is only just indicated in Amia, c conus arteriosus, fc valves, s sinus venosus, t cardiac aorta, v ventricle.—Orig. situated. All three sections are red, and their walls are furnished with striated muscle-cells. In the Teleostei, the conus is, as a rule, quite rudimentary (extremely short and without musculature), and is provided with but two valves; only in a few cases (from the family of the Herrings) is it somewhat more significant, although still very short; and in a single genus [Butirinus) there are two rows of valves.* In the Cyclostomes a conus is wanting. In Pisces there is usually a transverse row of valves between the auricle and ventricle, and between the sinus venosus {see below) and the auricle. From the anterior end of the conus, or of the ventricle when the former is absent, arises a longer or shorter cardiac aorta, which * In one of the Holostei, Amia, the conus is much shortened, and exhibits only three rows of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these
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