Chordate anatomy (1939) (20423882539)

Title: Chordate anatomy

Identifier: chordateanatomy00neal (find matches)

Year: 1939 (1930s)

Authors: Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-1960

Subjects: Chordata; Anatomy, Comparative

Publisher: Philadelphia : P. Blakiston's Son & Co.

Contributing Library: MBLWHOI Library

Digitizing Sponsor: MBLWHOI Library

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THE ANIMAL KINGDOM 17 of the latter are protected by fetal membranes, while those of the former are without them. Class Reptilia Reptiles are horny-scaled vertebrates which breathe by lungs. The embryos develop in a liquid-filled sac, the amnion. The skull articulates with the atlas vertebra by means of a single occipital condyle. Arterial and venous blood are mixed in the dorsal aorta. Living reptiles are divided into Rhynchocephalia, Lacertilia, Ophidia (Serpentes), Chelonia, and Crocodilia. Among fossil orders, the Thero- morpha are important, since, especially in their dentition, they resemble mammals, and the dinosaurs because they are the ancestors of the birds. Rhynchocephalia are mostly fossil reptiles having very primitive char- acteristics. Like some primitive amphibians they have only two sacral

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SPHENODON Fig. 19.—Sphenodon has been characterized as a "living fossil." Asa "primi- tive" type of reptile it interests the student of phylogenesis. It belongs to the Order Rhynchocephalia. vertebrae. Sphenodon (Hatteria), the only living representative, lacks the external copulatory organs present in all other reptiles. The Lacertilia are the lizards. They usually have two pairs of limbs; the anus is a transverse slit; eyelids and an external ear opening are usually present. Ophidia (Serpentes) are limbless reptiles devoid of movable eyelids and external ear-opening; the tongue is forked; the scales along the ventral side of the body are specially modified to assist in locomotion. Snakes. Chelonia (Testudinata) are toothless reptiles, the broad bodies of which are enclosed by a "shell" which consists of a dorsal carapace and a ventral plastron. The eyes have lids and nictitating membrane. Turtles and tortoises. Crocodilia have their teeth set in alveoli; the anus is a longitudinal slit; the tail is laterally compressed; the bodies are large. Alligators and Crocodiles. Theromorpha are fossil reptiles which may have been the progenitors of mammals; in some the teeth are differentiated as in mammals; the quadrate

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1939

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