Reptiles

(rép'tilz.) [From L. reptilis, creeping.] (Zool.) A cla of cool-blooded, oviparous,vertebrate animals, which are covered with scales, and which lay their eggs upon the land and whose young closely resemble the parents from the time they leave the shell. They breathe by lungs, have a heart with two auricles and one ven va tri cle, and their digestion is slow. The reptilian heart, at each of its contractions, transmits to DCI the lungs only a portion of the blood which comes to it from the various lu parts of the system, and the remainder goes into the circulation again without having been subjected to respira-up tion. Thus the blood of these animals is acted upon by oxygen far le than in Mammals and Birds, and their temperature is correspondingly lower, and their habits more sluggish. The smallne of the pulmonary ve els enables R. to suspend the proce of respira-Fig. 558. tion without arrest-ANATOMY OF THE LIZARD. ing the progre of a, a', arches of the aorta; r, right auri the blood; and cle; l, left auricle; v, ventricle; vcs, hence they are able venacava superior; vci, venacava in ferior; va, ventral aorta; pv, pulmonto remain much ary veins; pa, pulmonary arteries; lu. longer beneath the lung; li, liver and hepatic vein; k. surface of the water kidneys and renal ve els; up, vena than other animals. porta; s, stomach; int, intestines; an, anus. The cells of the lungs are le numerous, and larger, than in the higher animals. The brain of R. is comparatively small, and their sensations blunt. They continue to live and exhibit voluntary motions long after losing the brain, and even after the head is cut off. The muscles preserve their irritability for a considerable time after being severed from the body, and even the heart pulsates for hours after it is removed: nor does its lo prevent the animal from moving about. The vertebræ of R. are convex at one end and concave at the other; and their teeth, when set in sockets, never have more than one prong. This cla is divided into the three orders Testudinata (the Turtles), Sauria (the Lizards), and Ophidia (the Serpents). [s. 763]