THE FROG S HEART. 



77 



ganglia usually lie near the pericardium. In mammals, the two largest ganglia lie 

 near the orifice of the superior vena cava in birds, the largest ganglion (containing 

 thousands of ganglionic cells) lies posteriorly where the longitudinal and transverse 

 sulci cross each other. Fine branches, also provided with small ganglia, proceed 

 from these ganglia, and penetrate the muscular walls of the auricles and ventricles. 

 [Frog's Heart. The frog's heart consists of the sinus venoms, into which open the single 

 inferior and the two superior vense cavse (fig. 54). There are two auricles ; the right one com- 

 municates with the sinus venosus, and opens into the single ventricle ; the left auricle also 



A.s 



A.p,- 



Fig. 53. 

 Heart of frog from the front. V, single ven- 

 tricle ; Ad, As, right and left auricles ; 

 B, bulbus arteriosus ; 1, carotid, 2, aorta, 

 and 3, pulmo-cutaneous arteries ; C, ca- 

 rotid gland. 



Fig. 54. 

 Heart of frog from behind, s.v., sinus ve- 

 nosus opened ; ci, inferior ; csd, ess, right 

 and left superior vense cavse ; vp., pul- 

 monary vein ; Ad, and As, right and 

 left auricles ; Ap, communication between 

 the right and left auricle. 



opens into the single ventricle (fig. 53, v), and in the latter are mixed the venous blood returned 

 by the right auricle and the arterial blood from the left auricle. The aorta with its bulbus 

 arteriosus conducts the blood from the ventricle. The various orifices are guarded by projec- 



i'M/.T? 





Fig. 56. 

 Pyriform ganglionic bi-polar nerve-cell from 

 the heart of a frog, m, sheath ; n, straight 

 process ; o, spiral process. 



T B 



Fig. 55. 

 Auricular septum of a frog's heart, a, an- 

 terior, and p, posterior branch of the car- 

 diac vagus ; B, Bidder's ganglion. 



tions of tissue, which act like valves. The two auricles are completely separated by a septum. 

 This septum ends posteriorly in a free concave margin so as to divide the auriculo -ventricular 

 orifice into a right and a left orifice. Each orifice is guarded by two thick fleshy valves, which 

 close it] 



[Nerves. The two cardiac branches of the vagi the nervi cardiaci proceed to the posterior 

 surface of the sinus venosus, and where the latter joins the auricle they interlace, and are mixed 

 with a number of ganglion cells (fig. 57). This spot is called Remak's ganglion, is sometimes 



