. The elasmobranch fishes . Fig. 163. The developing branchial arteries, Squalus acanthias. (From Scammon.) ^''^, first and sixth embryonic aortic arches; af., first afferent artery; cl., gill cleft; ^, paired dorsal aorta; , dorsal aorta; ef., efferent artery; e/c", anterior efferent- collector; , posterior efferent-collector; ps., pseudobranchial artery; sp. spiracle; , ventral aorta; x., where break in primary arch will take place. We may briefly consider the formation of the afferent and efferent systems in the embryo of Squalus as described by Scammon (1911), The
. The elasmobranch fishes . Fig. 163. The developing branchial arteries, Squalus acanthias. (From Scammon.) ^''^, first and sixth embryonic aortic arches; af., first afferent artery; cl., gill cleft; ^, paired dorsal aorta; , dorsal aorta; ef., efferent artery; e/c", anterior efferent- collector; , posterior efferent-collector; ps., pseudobranchial artery; sp. spiracle; , ventral aorta; x., where break in primary arch will take place. We may briefly consider the formation of the afferent and efferent systems in the embryo of Squalus as described by Scammon (1911), The arterial system here consists of (1) a ventral aorta (, fig. 163) running forward from the heart under the gill region, (2) a dorsal aorta () extending backward above this and dorsal in position, and (3) six aortic arches ('^~^) connecting dorsal and ventral aortae in the pharyngeal or branchial region. Upon the formation of the gill filaments a new branch (e/c") is budded off which collects the blood from the newly formed gill tissues. The origin of this collector from the embryonic aortic arch marks the place where the embryonic arch later separates (see last arch at x) into two parts, the upper becoming the efferent (ef.) which joins the dorsal aorta, and the lower the afferent (), which joins the ventral aorta. The collector (e/c") (efferent-collector) next sends cross-trunks backward to the posterior demibranch and a posterior efferent-collector (efc.^) is formed. In the last arch it will be observed that the posterior efferent-collector has not as yet formed. In a general way it may be said that for every embryonic aortic arch, except the first and second, two ef- ferent-collectors thus arise. One of them is formed for the anterior demibranch (efc"), the other for the posterior (efc.^). The two collectors then continue to grow downward and the tip of the posterior efferent-collector now joins the
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