THE HEART. 



215 



appears to be absent (Fig. 135 >. 

 The septum is attached to the 

 walls of the auricles so as to 

 form two distinct cavities, which 

 communicate at the auriculo- 

 ventricular opening, where the 

 septum .has a free concave 

 border (Fig. 134). The right 

 is mnr\ largpr tnajl t" 



Fig- 134- 



C. 



PV. 



ives the sy-temig 

 is blood from the sinus 

 he opening (Figs. 

 133 and 134 SJ .) already de- 

 scribed. The left auricle_ re- 

 ceives the blood from the limits 

 by the pulmonary_ vein (Fig. 



133 PJ . }, which opens into the 

 auricle near the septum (Fig. 



134 Pr.) : [the openings from A 

 the sinus venosus and from B - 



The frog's heart seen from the ventral surface, and 

 dissected so as to show its structure. The ven- 

 tral walls of the truncos arteriosus and of the 

 auricles and ventricle have been removed. From 

 a drawing by Mr, Hurst. 



Anriculo- ventricular aperture and valve. 

 Aperture leading from ventricle to truneus 

 arteriosus. 



the pulmonary vein mav be so c. Left carotid arch. 



, LA. Left auricle. 



Closely approximated as to be p. Left pulmo-cutaneous arch. 



Separated bv the Sentum Onlv f> ' Style passed down right puhno-cutaneous arch 



uy lue septl lUiy. into the truncus arteriosus, T. 



The Septum is much thinner PV - Opening of pulmonary vein. 



, , r . , n T Tj 4.1 RA - Right auride. 



than the auricular wallsj. Jooth 5. Left systemic arch. 



auricles open into the ventricle | o^nTg^fSm^Venosu, into right auricle. 



by the auriculo-ventricular open- v - ventricle. 



ing (Fig. 134). 



c. The ventricle (Figs. 132, 134, and 136 7".), examined while 

 still living, is seen to be bluntly conical in 

 shape and darker on the left side than on the 

 right this is due to the ventricular wall of 

 the right side, near the truncus arteriosus, being 

 somewhat thinner. The inner wall is not smooth 

 but possesses muscular ridges (Tra$ecvlae). At 

 its base the ventricle communicates with the Dissection of a case in 

 auricles by the auriculo-ventricular opening 

 (Figs. 134 and 13.6 V, and with the truncus 

 arteriosus by a separate opening (Fig. 134 3 

 The ventricle is lined bv a layer of endocardial 55^ Left auricle, 

 endothelium. * v Opening into ^ 



which the auricular 

 septum ia placed more 

 to the left than is nor- 



