. Elements of comparative zoology. Zoology. 294 SYSTEMATIC ZOOLOGY. numerous in the lower and reduced by fusion or actual loss in the higher forms. In the sharks the visceral skeleton is very simple, being represented by the upper and lower jaws (Fig. 104, pq, ra) by the gill-arches or giil-bars, and by a few cartilages sup- porting the lips. The upper jaw is not firmly united to. iv b ill FIG. 104.—Diagram of the skull and branchial arches of a shark, h, hyoid; km, hyomandibular, forming the suspensor of the lower jaw, m (Meckel's car- tilage); pq, upper jaw (pterygoquadrate); s, spiracle; I-
. Elements of comparative zoology. Zoology. 294 SYSTEMATIC ZOOLOGY. numerous in the lower and reduced by fusion or actual loss in the higher forms. In the sharks the visceral skeleton is very simple, being represented by the upper and lower jaws (Fig. 104, pq, ra) by the gill-arches or giil-bars, and by a few cartilages sup- porting the lips. The upper jaw is not firmly united to. iv b ill FIG. 104.—Diagram of the skull and branchial arches of a shark, h, hyoid; km, hyomandibular, forming the suspensor of the lower jaw, m (Meckel's car- tilage); pq, upper jaw (pterygoquadrate); s, spiracle; I-V, gill-arches, between which are shown the gill-clefts. the cranium, but is held in position by muscles and liga- ments, and by the hyomandibular (hm), while the lower jaw is hinged to the upper, and not to the cranium. Com- parisons, which cannot be described here, show that the upper jaw of the shark is not the same as the upper jaw in the other vertebrates. In them numbers of other bones are added to the skull, and the upper jaw of the shark is only comparable to two pairs of bones, known to anato- mists as the pterygoids and the quadrates (fig. 105). hence the name pterygoquadrate cartilage used for this part in the sharks. The rest of the visceral skeleton consists of bars of cartilage on either side of the throat between the gill- slits, the series being united below (Fig. 104). These gill- arches serve to keep this region, weakened by the openings, from collapse. The most anterior of these gill-bars has the special name of hyoid (Fig. 104, h), and its upper part. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
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