The Development of the American Alligator; (A. Mississippiensis) with Twenty-Three Plates

The Development of the American Alligator; (A. Mississippiensis) with Twenty-Three Plates

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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. 1908 edition. Excerpt: ...the sectioned embryo was more nearly of the state of development of the embryo represented in figure 14, to be described later. Figure 13/?, about forty sections posterior to figure 130, passes through the hindbrain in the region of the ears. Being back of the region affected by cranial flexure, this section is of course of much less area than the preceding. The ectoderm shows no unusual features; it is of uniform thickness except where it becomes continuous with the entoderm around the mandibular folds (md); there it is somewhat thickened. The most striking feature of the section is the presence of two large auditory vesicles (0). The section being not quite at right angles to this part of the embryo, the vesicles are not cut in exactly the same plane; the one on the left is cut through its opening to the exterior, while the one on the right appears as a completely enclosed cavity. In a section a short distance posterior to this one the appearance of the vesicles would be the reverse of what it is here. As may be seen in the figure, the vesicles are large, thick-walled cavities lying close to the lateral walls of the hindbrain. The hindbrain itself has the usual triangular cross-section, with thick lateral walls and a thin, wrinkled dorsal wall. Close to the ventral side of the hindbrain lies the notochord (nt), on each side of which, in the angle between the brain and the auditory vesicles, is a small blood-vessel (bv). Ventral to these structures and close to the dorsal wall of the pharynx (ph) are the two large dorsal aortas (ao). The ventral side of the section passes through the open anterior end of the pharynx (ph). On the left is seen the widely open hyomandibular cleft (g'), between the main body of the section and the mandibular...show more

Product details

  • Paperback | 30 pages
  • 189 x 246 x 2mm | 73g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236834828
  • 9781236834829