. Journal of morphology. 4 cer. 5 Fig. 4 The principal structures of the hypobranchial region seen from anterior cartilage elements are displaced somewhat laterally and portions ofthe copulae omitted. 418 C. H. DANFORTH aorta. At the level of the third hypo-branchial cartilage itdivides into the two afferent arteries. One { 3) enters thethird gill in the same way as those described above, while theother { 4) reaches the fourth in what at first sight appearsa very unusual manner. It ascends in an obhque groove onthe lateral face of the second copula (fig. 5) to gain the
. Journal of morphology. 4 cer. 5 Fig. 4 The principal structures of the hypobranchial region seen from anterior cartilage elements are displaced somewhat laterally and portions ofthe copulae omitted. 418 C. H. DANFORTH aorta. At the level of the third hypo-branchial cartilage itdivides into the two afferent arteries. One { 3) enters thethird gill in the same way as those described above, while theother { 4) reaches the fourth in what at first sight appearsa very unusual manner. It ascends in an obhque groove onthe lateral face of the second copula (fig. 5) to gain the floor ofthe mouth where it is separated from the oral cavity only bythe mucosa and the shghtest amount of subjacent tissue (, A). It crosses dorsally the anterior end of the ventral carti-lage of the fourth branchial arch and then turns down in a grooveon the medial and posterior aspect of that cartilage to enter thegill along the m. obhquus ventralis IV, thus coming into corre- c. cer. 5 c. cer. 4 c. CO. 3 c. CO. 2. a. br. a. 4 a. br. a. 3 a. an. a. br. a. 4 Fig. 5 The origin and proximal relations of the fourth afferent branchialartery. spondence with all the more anterior afferent arteries. Caudadto the groove for the artery there is a ligament binding the branch-chial cartilage to the second copula, and this is interpreted byBridge (79) and Van Wijhe (82) as a second articulation. Suchan interpretation seems justifiable, and, if it be correct, bringsPolyodon into accord with Amia and Acipenser, in so far asthis point is concerned. In the third and fourth arches of Amiathe hypobranchial articulates with the copula near the floorof the mouth and with its ventral keel at a deeper level (fig. 6, B).The artery passes through the enclosure thus formed. WithPolyodon the same condition exists in the third arch, but inthe fourth, where the hypobranchial has disappeared or lost THE HEART AND ARTERIES OF POLYODON 419 its individuality, the ventral articulation is displaced forwar
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