KEPTILIA. 569 



part of the impure blood expelled from the ventricle is at once 

 driven to the organs of respiration to be further oxygenized. The 

 aorta) immediately after its origin, likewise separates into two 

 trunks (d, e), the right and the left ; which, winding backwards, 

 ultimately join to form one great vessel (/), from which the arteries 

 of the viscera (i, A:), and those destined to the posterior parts of 

 the body, are given off. From the commencement of the right 

 aortic trunk a very large vessel is furnished, "which bifurcates to 

 form two arteria innominate (g*, g), from which the carotid and 

 subclavian arteries take their origin. 



(628.) Although the above description refers more immediately 

 to the construction of the heart of the Tortoise, in all essential par- 

 ticulars it is equally applicable to all Reptiles of the Saurian, Che- 

 Ionian, and Ophidian orders ; and when we thus see that, in addition 

 to the comparatively imperfect condition of their lungs, the blood 

 which circulates through the body is in these creatures a mixed and 

 semi- venous fluid, we need not be surprised at the contrast which 

 they offer when compared with the hot-blooded and vigorous ani- 

 mals to be described in the subsequent chapters of this work. 



Cuvier committed a serious error in describing the Batrachian 

 Reptiles as having a heart composed but of two cavities : our illus- 

 trious countryman John Hunter had already ascertained that, in 

 Frogs, Toads, and Salamanders, the heart possessed a pulmonary 

 as well as a systemic auricle ; and his observations have since been 

 abundantly confirmed by Dr. Davy, Dr. Martin St. Ange, and 

 Professor Owen. The pulmonic auricle in these creatures is in- 

 deed comparatively of small size ; but it exists as a perfectly distinct 

 chamber, and receives the blood from the lungs preparatory to its 

 admission into the common ventricle. 



With regard to the use of the additional auricle in the Reptilia, 

 Professor Owen has well remarked,* that from the impediments which 

 frequently occur to a free and regular circulation of blood in these 

 cold-blooded and slow-breathing creatures, the venous side of the 

 heart is subject to great distension ; hence the large size of the auri- 

 cles, and of the sinus which receives the systemic veins, and also the 

 perfect developement of the valves intervening between the venae 

 cavse and the auricle, of which the Eustachian valve of the Mammi- 

 ferous heart still presents a rudiment. Had the pulmonary veins 

 terminated along with the systemic in the same cavity, their orifices 

 would have been subjected to the pressure of the accumulated con- 

 tents of that cavity, and there would have been a disproportionate 



* Transactions of the Zoological Society of London, vol. i. p. 217. 



