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Show 876 MR. W. WOODLAND ON THE [Nov. 27, species of the same genus and from most if not all other genera of the Squalidae. According to Gunther u, " the valves of the conns arteriosus of the heart" in C. squamalosus (and C. granulosus) " are arranged in five transverse series, each series consisting of three powerful valves and as many intermediate small ones" *. According to Stolir22, the conus of Acanthias vulgaris possesses four rows of valves, but three according to Midler11; in Lchino-rhinus spinosus, three rows according to Turner10, four according to Jackson & Clarke20; in Lcemargus borealis, four according to Turner14; in Squalus maximus, four according to Home 23; in Squalus catulus, two according to Stolir. The afferent arches (PI. LYI11. fig. 4) are similar in construction to those of the Common Dogfish : the " first" (first and second) dividing into two at some distance from the median line to supply the first two gill-clefts, the third arising from the ventral aorta nearly an inch below the first and supplying the third gill-cleft, and the " fourth " (fourth and fifth) arising just behind the third and emulating the " first " arch by dividing into two shortly after; these respectively supplying the fourth and fifth branchial clefts, and in this respect differing somewhat from Scyllium canicula. The afferent arches are the same in C. granulosus 10, save that the fifth afferent arches originate from the main ventral aorta, as in the Dogfish. The efferent arches have the disposition shown in fig. 5. The fourth pair arises about half an-inch in front of the coeliac artery, and by bifurcating in the usual manner supplies the fourth and fifth gill-clefts. The third and second have the same construction. Between the third and fourth arches the subclavian arteries arise. The first efferent arch forks over the first gill-cleft, and from the inner side of the fork gives off the common carotid which proceeds anteriorly and towards the median line until it meets its fellow of the opposite side and thence proceeds through the cartilaginous floor of the cranium to the brain. About a quarter of an inch from the junction of the two carotids, each gives off an external carotid (the portion of the carotid continuing towards the median line being termed the internal carotid) which runs through the cartilage to the inner wall of the orbit, where it divides into both anterior and posterior branches as shown in PI. LXI. figs. 16 & 17. The first efferent arches also give off', about half-an-inch from their origin, two small vessels which run forward for a short distance parallel to the vertebral column, and which possibly represent the primitive paired condition of the aorta. There is no hyoidean artery arising from the first efferent arch, such as exists in the Common Dog©fish. * According to both Muller and Owen, the presence offour tiers of valves in theconus is characteristic ot the genus Centrophorus- an obvious misstatement of the facts. 22 " Ueber den Klappenappavat im Conus arteriosus der Selachier und Ganoiden." Morph. Jahrb. Bd. ii. 1876. -* " An Anatomical Account of the Souahts maximus, &e." Phil. Trans, vol. xcix 1809. |