. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. THE SKULL 75 strongly projecting auditory regions. Labial cartilages are present in connection with the lips, nostrils, and jaws (Figs. 55, 56, and 57). The palatoquadrate is usually only united to the basis cranii by ligaments, but in the Chimseroids (Fig. 57) it becomes immovably fused with it, whence their name of Holocephali. In the Sharks ^nd Rays the palatoquadrate is not directly united to the skull, but is suspended from it by the hyomandibular (p. 70, Figs. 55 and 56). In this case the skull may be described a
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. THE SKULL 75 strongly projecting auditory regions. Labial cartilages are present in connection with the lips, nostrils, and jaws (Figs. 55, 56, and 57). The palatoquadrate is usually only united to the basis cranii by ligaments, but in the Chimseroids (Fig. 57) it becomes immovably fused with it, whence their name of Holocephali. In the Sharks ^nd Rays the palatoquadrate is not directly united to the skull, but is suspended from it by the hyomandibular (p. 70, Figs. 55 and 56). 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 (Fig. 57). A cleft, the spiracle, is situated in front of the hyomandibular, and leads into the cavity of the mouth; on its anterior wall may be found remnants of the embryonic spiracular gill, beneath which is a spiraeular cartilage (comp. p. 70, and Fig. 56). The branchial skeleton is always well developed, and owing to secondary segmentation and fusion of its parts exhibits char-. Fig. 56.—Skull of Skate. (After W. K. Parker.) Au, auditory capsule ; Na, olfactory capsule ; , prenasal rostrum ; , Qn, palatoquadrate bar ; Mch, mandibular (Meckel's) cartilage ; 21. Pt, spiracular cartilage ; , hyomandibular ; , interhyal ligament; , epihyal; , ceratohyal; , hypohyal; , 1, 2, 5, hypobranchials ; above them are seen the cerato-, epi-, and pharyngo-branchials ; //, optic foramen ; V, foramen for trigeminal and facial nerves. (The branchial rays and extra- branchials are not indicated.) acteristic modifications. On the outer circumference of each branchial arch, as well as on the hyomandibular and hyoid, radially- -arranged cartilaginous rays are situated, which serve as supports for the gill-sacs (Fig. 55). Externally to these rays small rod-like " extra-branchial" cartilages are present. In nearly all Elasmobranchs the gill-slits
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
