Srt 



mouths of great rivers for the purposes of respiration, and landing on the sand,' 

 daring the night, to deposit its ova. The individual from which the pre- 

 sent description is taken, weighed about 1751bs., the heart, when removed from 

 the body, and emptied of its blood, was about the size of a large lamb's heart, and 

 pulsated for six hours after death ; the contractions of the heart, after they had 

 apparently ceased, might easily be excited again by pricking it with the point 

 of a needle. This excitability continued during three or four hours more. 



The heart of this order of reptiles is composed of four cavities, like those of 

 the mammalia and birds ; two of the cavities receiving the blood from the body 

 and lungs, the other two propelling it forward into the lungs, and to the system 

 generally. Man and the higher orders of animals, as mammals and birds, have a 

 perfect double circulation, the heart consisting of four distinct and separate cavi- 

 ties ; two, the receiving parts, termed auricles, the propelling ones, called ventri- 

 cles. The reptilia (of which the Turtles and Tortoises form the first order) have 

 a circulation performed by an organ of a different anatomical construction : in 

 these animals the cavities are still four-fold, but the cavities of the ventri- 

 cles are not distinct from each other ; they have communications through which 

 the blood returning from the body generally, and that received from the lungs, are 

 intermixed, and consequently an imperfectly decarbonized fluid is sent to the eco- 

 nomy at large. The heart of the Testudo mydas, of which a general view is 

 given in Fig. 1, is composed of two auricles and two ventricles, a b and c d, like 



Fig. 1. 



Fig. 2. 



Fig. 1 — A front view of the heart, with the cavities of the right and left ventricles laid 

 open. a. The right auricle, b. The left auricle, c. The right ventricle. <L The 

 left ventricle, e. The pulmonary arteries. /. The aortse, three in number ; one 

 destined to supply the head, neck, and fore limbs, the remaining two uniting to sup- 

 ply the posterior half of the body. 



Fig. 2 — A back view of the heart, with the fissures, which mark the opening of the 

 veins, returning the blood from the body and the lungs, a. The opening of the veins 

 of the lungs into the left auricle. 6. The opening of the venae cavse returning the 

 blood from the body to the right auricle. 



