. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 0,i!iimi^'nm§. Fig. 6. Reconstruction of the head and shoulder girdle of two ptyctodonts; lateral view. A, Rhamphodopsis trispinofus Watson; B, Ctenurella glodbochens/s 0rvig. , Dorsal arcualio; , ventral arcualia; has., basal; bro., branchial arch; , ceratohyal; , dorsal spine; , epihyal; , labial cartilage; Mk., Meckel s cartilage; , nnandib- ular toothplate; , notochord; , pharyngohyal; pq., palatoquadrate; , upper toothplate; rpm., medial rostral process; rpp.,
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 0,i!iimi^'nm§. Fig. 6. Reconstruction of the head and shoulder girdle of two ptyctodonts; lateral view. A, Rhamphodopsis trispinofus Watson; B, Ctenurella glodbochens/s 0rvig. , Dorsal arcualio; , ventral arcualia; has., basal; bro., branchial arch; , ceratohyal; , dorsal spine; , epihyal; , labial cartilage; Mk., Meckel s cartilage; , nnandib- ular toothplate; , notochord; , pharyngohyal; pq., palatoquadrate; , upper toothplate; rpm., medial rostral process; rpp., paired rostral processes; , scapulocoracoid ossification; sp., spinale. (A after Watson; B after 0rvig.) genetischen Erwerb dar, der speciellen mechanischen Bediirfnissen ; All that can really be said with certainty is that the laliial cartilages are quite different from those of sharks in their number and fonn, and in having muscles inserted upon them, and that their present condition implies a long, separate evolution. The remainder of the axial skeleton is very much simpler to analyze than the skull, but no more directly indicative of the holo- cephalians' ancestry. The vertebral column presents certain distinctive characteristics which may be listed in a straightforward manner. Anteriorly, it is consolidated rad- ically—not only are the first two or three vertebrae fused with the cranium, but the first seven elements posterior to the occip- ital articulation are broadly fused with each other to support the strong dorsal spine and an accompanying basal fin-cartilage. True centra are never present; in the notochord is unconstricted; in Wiino- chimaera and Chirnaero cartilaginous rings develop within the notochordal sheath. Rabinerson (1925), who studied the com- parative anatomy of the vertebrae of carti- laginous fishes, was of the opinion that the Holocephali were distinct from the selachi- ans in the development of these elements. He
Size: 1878px × 1331px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorharvarduniversity, bookcentury1900, booksubjectzoology
