. The Cambridge natural history. Zoology. 220 FISHES extra-branchial cartilages of an Elasmobranch than with the more deeply-seated branchial arches. While the skull of the Myxinoid Cyclostomes ^ is constructed on the same general lines as that of the Lamprey, it is in some respects more primitive. It is also clear that in other features the skull has undergone marked specialisation on lines of its own, and in some points again it seems to deviate less from the more normal Craniate type. Of the more obvious differences, as illustrated by the skull of Bdellostoma (Figs. 125-127), it will. Fig.
. The Cambridge natural history. Zoology. 220 FISHES extra-branchial cartilages of an Elasmobranch than with the more deeply-seated branchial arches. While the skull of the Myxinoid Cyclostomes ^ is constructed on the same general lines as that of the Lamprey, it is in some respects more primitive. It is also clear that in other features the skull has undergone marked specialisation on lines of its own, and in some points again it seems to deviate less from the more normal Craniate type. Of the more obvious differences, as illustrated by the skull of Bdellostoma (Figs. 125-127), it will. Fig. 125.—Side view of the skull of Bdellostoina ; the gill-apertures and their cartilages have been omitted. A, Auditory capsule ; B, B', B", the anterior, middle, and posterior segments of the lingual bar ; 6', cartilage connecting the hyoid arch with the second branchial arch ; br^, br'^, first and second branchial arches ; , coronal cartilage; Or, cranium; D, dental plate ; dt, median dorsal tooth; , ex- ternal part of the naso-pituitary canal ; jlp, plate ; Hy, hyoid arch ; N. subnasal cartilage ; nc, neural canal ; Nt, notoehord ; OC, olfactory capsule ; PL, palatine portion of the palato - quadrate cartilage PQ; S, supra-pharyngeal plate supporting the velum ; t, tendon of the retractor mandibuli muscle ; t\ t'^, t^, tentacular cartilages ; t*, cartilage supporting mouth lobe ; tr, trabecula ; F^, rod connecting S with the inner surface of the hyoid arch of its side ; V, outer lateral rod which joins F'; 1, 2, 3, fenestrae. (Modified from Ayers and Jackson.) be sufficient here to mention the following: (i.) The more primitive condition of the chondrocranium, the roof and side walls of the cranial cavity being entirely membranous, (ii.) The non-develop- ment of a suctorial buccal funnel and the presence of oral tentacles, associated with the absence of the complex system of labial cartilages and the substitution of a special tentacular skeleton, (i
Size: 2782px × 898px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
