256 



THE HUMAN BODY. 



plied from both auricles and having projecting into it the two 

 flaps of the auriculo-ventricular valve, which are continued 



from the end of the septum 

 or partition lying between 

 the auricles; the bulbus ar 

 teriosua, E, from which the 

 systemic and pulmonary arte- 

 ries are supplied. To describe 

 the very interesting mechan- 

 ism by which the arterial and 

 venous blood supplied to the 

 single ventricle are kept sep- 

 arate and sent from the arte- 

 rial bulb through different 

 channels would take us be- 

 yond the limits of this book, 

 but it is well worth study in 

 some treatise on comparative 

 physiology. 



The muscular tissue of the 

 frog's heart consists of cells 

 which are in form somewhat 

 like those of involuntary mus- 

 cle, but they are frequently 

 forked at their ends, and they 

 are obscurely cross - striped 

 like human cardiac muscle 

 (Fig. 123). The main thick- 

 ness of the walls of all the 

 chambers of the heart consists 

 of this muscle, and is known 

 as the myocardium. It com- 

 mences on the ends of the 



Flo. 99. Diagram of the frog's heart, ~ ra of VPITKS npm* whprp thpv 

 A, venous sinus; B, C, right and left au- great Veins liey 



ricies, together forming the atrium ; p ., -j o j n the heart, and is thence 



pulmonary veins; a, a, constriction be- J 



tween sinus and atrium; D, ventricle; continued to the roots of the 

 g, 0, constriction between auricles and . .... , 



ventricles; i, auriculo-ventricular valve; great arteries arising irom the 

 E, arterial bulb; P, pneumogastric or f . ,. , ,-, 



vagus nerve; S, sympathetic nerve; N, bulb; but it IS thinner at the 

 cardiac nerve containing fibres from both . ,. , . -, r -, 



vagus and sympathetic. Z shows the COllStriCtlOUS Which 116 De- 

 natural relative positions of the chief , rn -_ f r._ ^o^ ncnrifipa fVian 

 chambers of the heart: d, vena cava; e, tween the main Cavities tnail 



?SSflBfcf >/f ^* l " ;le; elsewhere, and there is ar- 



ranged in rings around the openings. 



