. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. TIM<: SKULL. G5 The olfactory sacs lie in the ventro-lateral parts of the nasal region, which is often elongated to form a long cut-water or rostrum (intertrabecula). Behind this are seen the deep orbital hollows (Figs. 50 and 51), which are bounded posteriorly by the strongly projecting auditory regions (GK]. The palatoquadrate is usually only united to the basis cranii by ligaments, but in the Chimaorae it becomes immovably fused with it, whence their name of Holocephali. In some forms, the
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. TIM<: SKULL. G5 The olfactory sacs lie in the ventro-lateral parts of the nasal region, which is often elongated to form a long cut-water or rostrum (intertrabecula). Behind this are seen the deep orbital hollows (Figs. 50 and 51), which are bounded posteriorly by the strongly projecting auditory regions (GK]. The palatoquadrate is usually only united to the basis cranii by ligaments, but in the Chimaorae it becomes immovably fused with it, whence their name of Holocephali. In some forms, the palatoquadrate is not directly united to the skull, but is suspended from it by the upper segment of the hyoid arch or hyomandibular (Fig. 51, Hm). In this case the skull may be described as hyostylic, to distinguish it from autostylic skulls, in which the hyoid takes no part in the suspensorium.' ~A cleft, the spiracle, lies on the anterior border of the hyomandibular, and leads into the cavity of the mouth, and on its walls may be found remnants of the embryonic spiracular (mandibular) gill. The branchial skeleton is always richly developed, owing to secondary segmentation and fusion of its parts, and exhibits characteristic modifications. On the outer circumference of each branchial arch radially-arranged cartilaginous rays are developed, 7? FIG. 51.—CRANIAL SKELETON OF Raja oxyrhyncha. OK, auditory capsule ; Orb, orbit; NK, nasal capsule ; It, rostrum ; LK, ZA'1, labial cartilages ; Sp, spiracular cartilage ; SP[, spiracle ; PQ, palatoquadrate ; Mel, mandible ; Hm, hyomandibular ; hy, hyoid ; 1 to /', first to fifth branchial arches ; a, b, c, d, the individual segments of the branchial arches, viz. the pha- ryngo-, epi-, cerato-, and hypobranchials ; t, point of union of the fourth and fifth branchial arches ; Cp, basibram-hials. which serve as supports for the gill-sacs. They are present also on the hyomandibular and hyoid, and rudiments of mandibular rays are pre
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Keywords: ., bookcentury1800, bookdecade1880, bookpublisherlondonnewyorkmacmi
