538 



GENERAL CHARACTERS OF REPTILES. 



o ward the heart, goes to empty itself into the descending aorta (00} 

 It follows from this, that at each contrac- 

 tion of the heart, one portion of the 

 venous blood is carried to the lungs, and 

 another portion goes to be mixed with 

 arterial blood ; but this mixture is not 

 carried on in the first part of the interior 

 of the aorta, but below the origin of the 

 branches (c c) which this vessel sends to 

 the head and anterior part of the body, 

 so that these parts receive pure arterial 

 blood ; whilst all those parts, whose 

 arteries arise below the point of junc- 

 tion of the aorta, with the vessel arising 

 from the right ventricle, only receive 

 a mixture of red and dark blood. 

 With respect to the mode of distribution 

 of the arteries among Reptiles, we shall 

 only add, that there exist two or more 

 aortic arches curving to the right and 

 to the left, and shortly uniting to con- 

 stitute one trunk (Fig. 314). 



479. The respiration of Reptiles is 

 not active ; the greater number of these 



animals consume but little oxygen, and can be deprived of it for 

 a long time without being suffocated. Moreover, temperature 

 has very great influence upon this phenomenon ; and in warm 

 weather, the necessity of respiration is felt much more than in 

 winter. The lungs are organised in a manner which is not fa- 

 vourable to a great activity of their functions ; for their air-cells 

 are very large, and consequently the vascular surface destined to 

 receive the contact of the air is of small extent (ANiM. PHYSIOL., 

 312). They are not lodged in a distinct cavity; the thorax 

 not being separated from the abdomen by a diaphragm ; and the 

 air is renewed in their interior with less facility and regularity 

 than in the higher animals. Sometimes even, as in Tortoises, 

 the absence of the ribs, or the immobility of these bones, renders 



09 



FIG. 313 TTfART AND LARGE 

 VESSELS OK CROCODILE. 



vv, systemic veins, termi- 

 nating in the right auricle, 

 Od ; vt, the two ventricles, 

 separated by an internal par- 

 tition ; ap, the two pulmo- 

 nary arteries, conveying blood 

 from the right ventricle to 

 the lungs ; a, trunk from the 

 same ventricle, going to join 

 the descending aorta ; vp, 

 pulmonary veins, emptying 

 into left auricle, og,- ao, aorta, 

 arising from left ventricle ; 

 c, c, vessels proceeding to 

 the head. 



