Elementary text-book of zoology Volume 2
Carl Friedrich Wilhelm Claus
Paperback
(RareBooksClub.com, March 6, 2012)
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1885 Excerpt: ...basi-arid supra-occipital remain as small cartilaginous tracts. There is also a parasphenoid on the base of the skull (fig. 622, Ps). The large exoccipitals (Ocl) (fused with the opisthotic) articulate by means of two condyles with the first vertebra, as in the Mammalia. The projecting auditory region is pierced by the fenestra ovalis, and the bone in its anterior part corresponds to the prootic (Pe). The lateral walls of the skull remain cartilaginous, but in the ethmoid region there is a ringshaped bone--the girdle bone, or sphen-ethmoid. For a fuller account of the development of the Amphibian vertebral column, vide Balfour, " Comparative Embryology," vol. ii., p. 456 et seq. As in Lepidosiren the mandibular arch is firmly connected with the skull. The mandibular suspensorium and the palato-quadrate are in direct connection with the cartilaginous cranium, and form on either side a wide outstanding infra-orbital arch, the anterior end of which either remains free or fuses with the ethmoid cartilage. The ossification appearing at the end of the suspensorium gives rise to the quadrate, while a membrane bone, almost hammer-shaped and overlying the suspensorial cartilage, is called the squamosal or perhaps more correctly tympanic (Ty). Two membrane bones extend forward along the lower side of the palato-quadrate bar--the pterygoid (Pt) behind and the palatine (PI) in front. The palatine is transversely placed behind the vomer. The outer arch of the upper jaw, formed by the prcemaxillary and maxillary bones (Jmx, Mx) may by means of a third posterior bone--the quadrato-jugal (J)--be continued back to the quadrate, but in many Perennibranchiata it is incomplete, the maxillaries being absent. The skeleton of the visceral arches is more or less consider...