80 ANTHROPOLOGY. 



The blood, after passing througli the lungs, is brought back to the left auri- 

 cle, which, contracting at the moment when the left ventricle is expanding, 

 forces the blood into the left ventricle. The contraction of this ventricle 

 drives the blood into the aorta, its reflux into the auricle being prevented 

 by the mitral valve. The semilunar valves of the pulmonary artery and 

 aorta prevent the reflux of blood into their respective ventricles. 



PI. 130, ßg. 1, right half of the heart from before: ', right auricle; '', right 

 ventricle. Fig, 2, left half of the heart from before : ', left auricle ; % left 

 ventricle. Fig. 4, larynx, trachea, pericardium, and lungs : \ pericardium. 

 Fig. 0, heart from before : ', right sinus ; % right auricular appendage (the 

 two constituting the auricle) ; ', superior vena cava ; ', inferior vena cava ; 

 '' % left sinus and appendage, or left auricle ; '• *, pulmonary veins ; ', sulcus 

 transversalis ; '", longitudinal furrow or fissure ; ", right ventricle ; ", pul- 

 monary artery ; ", left ventricle ; '*, aorta. Fig. 6, section of the right half 

 of the heart : ', right auricle ; ", fossa ovalis ; ', Eustachian valve ; ', open- 

 ing of the great coronary vein with the valvula Thebesii ; % right ventri- 

 i;le with its columnae carnea3 ; ", a point of the tricuspid valve with the 

 chordae tendineos ; ', pulmonary artery with two of the semilunar valves. 

 Fig. 7, section of the left half of the heart : ', left auricle with the open- 

 ings of the pulmonary veins; ', left ventricle; % mitral valves; ', aorta 

 Avith two semilunar valves. Fig. 8, direction of the muscular fibres of 

 the heart : '' "' ', fibres of the auricles ; \ fibres of the ventricles ; ', open- 

 ings for the large vessels of the heart; ', place where the fibres twist 

 round each other at the apex, to become united with the deep layers ; 

 ', place where the superficial anterior and posterior fibres interlace and 

 become united with the deep fibres ; *' ', openings of the pulmonary artery 

 and aorta. 



2. Special Anatomy of the Arteries. 



The aorta, situated on the base of the heart, may be considered as the 

 main trunk of a tree, whose ramifications ever increasing constitute the 

 arteries, the ultimate branches being the capillaries. The various arterial 

 divisions are named partly from their regional situation, as subclavian, 

 axillary, &c., partly from their relative position, as deep or superficial, 

 and partly from their distinction, as cerebral, ophthalmic, &c. The 

 names "aorta" and "artery" show the opinion entertained by the 

 ancients with respect to their functions, being supposed to conduct vital 

 air exclusively, from being found empty of blood after death, yet still 

 distended. 



The arterial tubes are of a dense structure, and when empt}- preserve 

 their form without collapsing. They are composed of three principal coats 

 or tissues. The first or externa/, is fibro-cellulai', strong and resisting, and 

 connects the vessels with the surrounding parts. The second, or middle, or 

 proper coat of the arteries is thickest, and consists of yellowish and rather 

 dry fibres, elastic but not brittle ; although circular they do not form cora- 

 786 



