Memoirs of the New York State Museum Volume 10

Memoirs of the New York State Museum Volume 10

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1907 edition. Excerpt: ...A rig. 11 Detached median occipital detached specimen of the median occipital show plate of Macropetalichthys showing ( m tensory canals and partially de-ing confluent canal systems is represented in text nuded ornamentation. Original in Mus. Comp. Zool. Nat. size fifJUTC 2 1. Evidence of the primitive nature of this genus, as compared with other Arthrodires, is furnished by the following characters, which point to a survival of embryonic or ancestral conditions: (i) continuity of the sensory canal systems; (2) discreteness of the central elements and their separation on either side of the middle line by the median occipital; (3) reduced number of median series of plates; and (4) absence of any evidence of articulation or other connection between the head shield and dorsal body plates. We have next to speak of the configuration of the basis cranii, by which term is understood, of course, not the inner surface of the cranial buckler, but the floor and posterior wall of the chondrocranium, the passageway provided for the initial portion of the vertebral axis, ossified parachordal cartilages, and the greatly elongated parasphenoid which forms the roof of the mouth. In the first place it should be noted that a bony extension of the external occipitals is developed along the posterior margin of the head shield in the form of a thin lamina or septum which extends nearly vertically downwards into the soft parts until reaching the level of the parasphenoid, with whose hinder extremity it joins. It is along the plane of this septum that the exoccipito-central canals penetrate downward and inward from the outer surface by means of funnel-shaped openings, the interior of which is filled with cancellated bony tissues. The function of the posterior...
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Product details

  • Paperback | 68 pages
  • 189 x 246 x 4mm | 141g
  • United States
  • English
  • black & white illustrations
  • 1236792866
  • 9781236792860