. Chordate morphology. Morphology (Animals); Chordata. PROTOPTERUS Figure 11-17. Aortic arches of Neocerotodus, A, and Protopterus, B, as seen in lateral view (semi- diagrammatic). (In port after Goodrich, 1930) 1 1-20 E). The efferent vessels differ somewhat from those observed in the actinopterygian in that there are two per arch and the stem vessels drain adjacent ^ill bars (Figure 11-21). This style of drainage is suggested in Anna and Neocerotodus. CUamydoselachus resembles the teleost in having the mandibular arch connected with the hypobranchial ef- ferent of the hyoid arch. It is disti
. Chordate morphology. Morphology (Animals); Chordata. PROTOPTERUS Figure 11-17. Aortic arches of Neocerotodus, A, and Protopterus, B, as seen in lateral view (semi- diagrammatic). (In port after Goodrich, 1930) 1 1-20 E). The efferent vessels differ somewhat from those observed in the actinopterygian in that there are two per arch and the stem vessels drain adjacent ^ill bars (Figure 11-21). This style of drainage is suggested in Anna and Neocerotodus. CUamydoselachus resembles the teleost in having the mandibular arch connected with the hypobranchial ef- ferent of the hyoid arch. It is distinctive in having the first si.\ arches represented and a seventh as well. In Squalus or Mustelus the mandibular afferent reaches only to the angle of the mouth; the afferent pseudobranchial comes from the efferent hyoid. The pseudobranch thus receives oxygenated blood. The development of the arches in Squalus has been studied (Figure 11-20). Six arches appear and for a time all are pre- sent. With the separation of afferent and efferent divisions, the mandibular arch becomes connected, below the level of the gill pouches, with the first branchial efferent. With this connective now supplying blood to the mandibular arch, the mandibular afferent stem atrophies. Presence of a single ef- ferent in each arch in the young shark suggests that this is the primitive condition; the two efferents of the adult rep- resent a modified state. Hydrolagus agrees with the actinopterygian fish in having four complete arches which serve the four gill openings (Figure 11-22). There is a hyoid hemibranch in front and a fifth hemibranch behind. The hyoid hemibranch is supplied by the second afferent arch. The efferent vessel joins the ef- ferent mandibular stem or the efferent hypobranchial of the first branchial arch to supply the mandibular and throat areas. Hydrolagus has only a single afferent and efferent ar- tery in each bar, and the efferent arteries are not joined above the gill pouches as in
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