. Journal of morphology. d to the afferent hyoidean artery of otherganoids and selachians. With teleosts, although sometimespresent in young (, Ameiurus, Salmo), it appears typicallyto be absent in the adult. In Polyodon I have frequently beenunable to find it, so its absence may here be a more or less com-mon anomaly—an anomaly which might perhaps be expectedon physiological grounds inasmuch as this artery can distributeonly venous blood to the tissues. The first afferent branchial artery, after having passed underthe tendon of the sternohyoideus, turns obliquely outward andbackward to en
. Journal of morphology. d to the afferent hyoidean artery of otherganoids and selachians. With teleosts, although sometimespresent in young (, Ameiurus, Salmo), it appears typicallyto be absent in the adult. In Polyodon I have frequently beenunable to find it, so its absence may here be a more or less com-mon anomaly—an anomaly which might perhaps be expectedon physiological grounds inasmuch as this artery can distributeonly venous blood to the tissues. The first afferent branchial artery, after having passed underthe tendon of the sternohyoideus, turns obliquely outward andbackward to enter its gill along the posterio-ventral border ofthe m. obliquus ventralis I (). The second enters itsgill in exactly the same way except that it goes dorsal instead ofventral to the tendon (fig. 4). The trunk () on either side which supplies the third andfourth gills runs back near the median line and dorsal to the THE HEART AND ARTERIES OF POLYODON 417 a. hb. y a. br. a a. hb. 4 a. Ihb. a. br. a. 4 m a. Ihb. m. obv. 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 cor
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Keywords: ., bookcentury1900, bookdecade1, booksubjectphysiology, bookyear1912
