. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CIRCULATION. 643 Reptiles.—The structure and functions of the circulatory organs in Reptiles form a sub- ject of great interest on account of the nume- rous varieties which they exhibit in different orders and genera, for in this respect the class of Reptiles may be said to present to us an anatomical analysis of the circulatory and re- spiratory organs, and to constitute a gradually simplifying series of forms, the observation of which enables us to trace in the most clear and interesting manner an analogy and correspon
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CIRCULATION. 643 Reptiles.—The structure and functions of the circulatory organs in Reptiles form a sub- ject of great interest on account of the nume- rous varieties which they exhibit in different orders and genera, for in this respect the class of Reptiles may be said to present to us an anatomical analysis of the circulatory and re- spiratory organs, and to constitute a gradually simplifying series of forms, the observation of which enables us to trace in the most clear and interesting manner an analogy and correspon- dence between the forms of these organs in warm-blooded animals and in fishes, which, but for the study of their structure in reptiles, must very probably ever have remained hidden from our view. In Fishes the heart consists of one auricle and one ventricle, and a single current of blood only passes through it. The structure of the heart is very similar in some of the Batrachia breathing by gills, but among other reptiles, we find a gradual transition in the form and structure of the heart from that just mentioned as peculiar to animals with aquatic respiration, to the double heart possessed by warm-blooded and air-breathing animals. Among the Reptiles provided with lungs and breathing air, some, as the Sauria, Ophidia, and Chelonia, have the ventricular part of the heart partially divided into two cavities (Jig- 314, Fig. Heart of Lacerta ocellata. H, H'J which correspond in structure, relative situation, and connections to the right and left ventricles of the heart of warm-blooded ver- tebrata; the anterior or right compartment (H'} giving off chiefly the pulmonary (P), the left or posterior ( H), the systemic arteries (A). In the others, viz. the Batrachia and Protean reptiles, the ventricle forms a single cavity (figs. 317 and 318, H), and gives origin to one large artery only (A), so that the pulmo- nary and systemic arteries derive their blood from the same tru
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