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AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



what similarly situated rounded aperture in the left auricle, that 

 of the pulmonary veins. The auricles have a common opening 



into the ventricle, guarded 

 by two flaps, a dorsal and 

 a ventral, which project 

 into the ventricular cavity, 

 and are attached to its 

 walls by numerous minute 

 fibrous strings. This 

 auriculo- ventricular valve 

 is imperfectly divided into 

 two by the free posterior 

 edge of the auricular sep- 

 tum, which is attached 

 above and below to the 

 flaps. 



The relatively small 

 cavity of the ventricle is 

 transversely elongated, and 

 the ventricular wall is 

 spongy. The auricles open 

 into the left side, and the 

 truncus arteriosus out of 

 the right side of its front 

 The latter opening 

 three semilunar 

 valve*, small membranous 

 pouches with their con- 

 cavities towards the trun- 

 cus. This is divided into 

 two parts (1) the pylan- 

 gium (into which the aper- 

 ture just mentioned opens) r 

 separated by another set 

 of semilunar valves from 

 (2) the excessively short 

 synangium. The cavity of 

 the pylangium is imperfectly divided into right and left halves 

 by a sinuous longitudinal flap attached to its dorsal wall, and to* 

 one of the anterior semilunar valves, but possessing a free ventral' 



end. 



Fig. 54 AUTERTES OF FROG (after EcJcer). 

 R.A, Right auricle; L.A, left auiicle; 

 V, ventricle; t.a, truncus arteriosns ; 

 c.a, carotid arch ; c.gt, carotid gland ; 

 <, carotid artery; La, lingual artery; 

 II., systemic arch ; o-v, occipito- verte- 

 bral artery ; o<; occipital artery ; vr, 

 vertebral artery ; s.d, subclavian artery ; 

 III., pul mo cutaneous arch; pf, pulmo- 

 nary artery ; ct, cutaneous artery ; d.ao, 

 dorsal aorta; cm-m, cceliaco mesenteric 

 artery ; u-cj, urinogenital arteries ; i/, 

 iliac arteries ; sc, sciatic arteries. 



