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Show 1906.] ANATOMY OF CENTROPHORUS CALCEUS. 881 jill correctly represented, as my figs. 6 & 16 (Plates LVLII. ifc LXI.) show when compared with his. The liyomandibular cartilage is, as shown by Gegenbaur, quite separate from the lower jaw, and is only indirectly attached thereto by a broad ligament (fig. 6). Slender ligaments also attach the hyomandibular to the hind extremity of the upper jaw, and the middle of the upper jaw to the hind part of the lower jaw (fig. 6). The upper jaw is apparently held in its place solely by means of its ligamentous attachment to the hyomandibular cartilage and by the large process above mentioned which was loosely inserted into the cartilaginous roof of the orbit. I did not detect any ethmo-palatine ligament. As Gegenbaur states, there are three pre-spiracular cartilages (my fig. 6) situated in the front wall of the large spiracular cleft1". In connection with the upper jaw there are two labial cartilages (enclosed in the folds of skin at the sides of the mouth shown in fig. 4, PI. LVIII.) and with the lower jaw one, on each side (fi.2-. 6). A prominent vertical ridge of cartilage is situated in the median line on the dorsal surface of the spatulate snout (PI. LX. fig. 15). With regard to the vertebral column of C. calceus, my figs. 7 & 8 (PI. LVIII.) supply all the information necessary. The vertebrae are of the ordinary cyclospondylous type; the apertures for the exit of the dorsal and ventral branches of the spinal nerves are respectively situated on the intercalary neural plates and the neural plates proper, and there is in transverse section a small canal situated at the base of the neural spine, as in some other Selachians 31, which contains a band of elastic fibres running the whole length of the body dorsal to the spinal cord. In the anterior dorsal fin, the skeleton of which is represented in fig. 9 (PI. LIX.), the large anterior spine does not reach ventrallv to the vertebral column, whereas in the posterior dorsal (PI. LIX. fig. 10) it is firmly grafted on, with a small cartilage situated immediately in front of it and on top of the vertebral column. The dorsal skeleton of the caudal fin consists, as shown (fig. 10), of a row of small inclined cartilaginous rods, two of these somactids abutting on each intercalary neural plate of the caudal vertebra; ventrally the haemal spines are prolonged. At the anterior extremity of the ventral caudal fin four cartilages are present distinct from the haemal spines, and, since the cerato-trichia are in this region attached to these and not directly to the haemal arches, these four cartilages probably represent a vestige of the anal fin. The skeleton of the paired fins is represented in figs. 11 & 12 (PI. LIX.). The pectoral fin is dibasal and possesses a few fringing cartilages on its posterior border. 30 See Ridewood for a comparative study of this region of the skull in Selachians: " On the Spii'acle and Associated Structures in Elasmobranch Fishes," Anat. Anzeig. Bd. xi. (14) 1895. 31 tk Das Naturliche System der Elasmobranchier auf Grundlage des Banes und der Entwicklung ihrer Wirbelsaule." C. Hasse. Jena, 1872. |