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Show 1899.] BLOOD-VESSELS OF TELEOSTEAN FISHES. 949 on the left, and the origin of the coeliaco-mesenteric artery is nearer the middle line than in Hippoglossus. In Mugil (fig. 8) the circulus cephalicus is considerably longer than broad, and the coeliaco-mesenteric artery arises from the median aorta behind the entry of the third and fourth branchial vessels, and not as in the two preceding genera. In Osmerus (fig. 10) and Albida (fig. 11), also, the coeliaco-mesenteric artery arises from the median aorta, but the subclavian arteries take their origin immediately behind the point of entry of the common trunk of the thud and fourth branchial vessels into the aorta, and not behind the coeliaco-mesenteric artery as in Mugil. In Scopelus the circulus cephalicus is small and nearly circular in shape, and the portion of median aorta intervening between its posterior angle and the mesial ends of the common trunks of the last two branchial vessels is unusually long. In Malapterurus (fig. 12) and Esox (fig. 15) the cceliaco-mesenteric artery arises from the aorta immediately ventral to the mesial ends of the common trunks of the third and fourth vessels; in Cyprinus (fig. 13), Cobitis (fig. 14), and Marcusenius it arises more posteriorly, and in Anguilla (fig. 16) considerably farther back. Except in this latter respect, the arrangement of the vessels in Marcusenius very closely resembles that of Esox. Judging by the excellent figure of Tinea published by Hyrtl (7. pl. iv.), this genus exactly resembles Cyprinus in the disposition of the vessels of the efferent branchial system. The efferent vessels of Cyprinus were figured by Duverney (6. pl. ix. figs. 17 & 18) nearly 140 years ago ; and although the figures are incomplete, the essential features are correctly represented. In Cyprinus, and according to Hyrtl in Tinea also, there are two pairs of subclavian arteries. The anterior pair, arising in front of the common trunks of the last two branchial vessels, supply the upper part of the pectoral arch, the posterior pair the lower part of the arch and the pectoral fins. A somewhat similar arrangement obtains in Esox. The mode of origin of the anterior pair has been remarked by Midler, and quoted by Stannius (22. p. 103, footnote 3) and Owen (18. p. 270, and 19. p. 489), and these vessels are shown, although not named, in Maurer's figure (13. pl. xi. fig. 1). The circulus is large in Malapterurus and Anguilla; and in the latter genus a median vessel, occupying the position of the anterior continuation of the primitive median aorta described in Selachian fishes by Ayers (4), may be traced forward from the posterior angle of the circulus. It soon forks, and is ultimately lost in the mucous membrane of the roof of the pharynx. In Anguilla, also, the origin of the posterior carotid artery is much farther removed from the entry of the first branchial vessel into the circulus than is usual. Meckel has stated (14. p. 193) that in the marine Eel, Murcenophis helena (Murcena lielena), the anterior lateral trunk formed by the union of the. first and second branchial vessels is three times as long as the posterior one formed by the union of the third and fourth. |