PHYLUM CHORDATA 



279 



puLcu-Zr 



the coelomic cavity between the gullet above and the epicoracoids 

 below ; it consists, as usual, of a visceral layer closely adherent to 

 the heart, and a loose 

 parietal layer, the two 

 being continuous at the 

 bases of the great ves- 

 sels and separated by a 

 small quantity of peri- 

 cardial fluid. 



The heart consists of 

 a sinus venosus (Figs. 

 929 and 933, s. v.), right 

 and left auricles (r.au., 

 I. au.), a ventricle (v.,vt.), 

 and a conus arteriosus 

 (c. art.). The sinus 

 venosus opens into the 

 right auricle, the pul- 

 monary veins into the 

 left: a striking advance 

 on the Dipnoi is seen 

 in the greatly increased 

 size of the left auricle 

 and its separation by 

 a complete partition, 

 the septum auricularum 

 (Fig. 931 ,spt.aur.), from 

 the >jpight. The two 

 auricles open by a com- 

 mon auriculo-ventricular 

 aperture, guarded by a 

 pair of valves (au. v. v.), 

 into the single ventricle. 

 The latter has a trans- 

 versely elongated cavity, 

 and its dorsal and ven- 

 tral walls are raised up 

 into muscular ridges or 

 trabeculse with inter- 

 stices between them. 

 The conus springs irom 

 the right side of the ly^ 

 base of the ventricle ; 

 it is separated from the 



latter by three small semilunar valves (v.), and is traversed 

 obliquely along its whole length by a large flap-like longitu- 

 dinal valve (J. V.) which springs from its dorsal wall and is free 



s 2 



Fig. 932.— Rana temporaria. The arterial system, 

 with the heart, lungs, kidneys, and left testis, from 

 the ventral aspect, car. carotid artery ; car. gl. carotid 

 labyrinth ; c. art. conus arteriosus ; car. tr. carotid trunk ; 

 ccfl. vies, coeliaco-mesenterifr' artery ; cm. cutaneous 

 artery ; d. ao. dorsal aorta ; du. duodenal artery ; ffs. 

 gastric artery ; Ji'p. hepatic artery ; ii. iliac artery ; 

 int. intestinal arteries ; kd. kidney; I. au. left auricle ; 

 Ig. lingual artery ; Ing. lung ; as. oesophageal artery ; 

 pul. pulmonary artery ; put. cu. tr. pulmo-eutaneous 

 trunk ; r. au. right auricle ; 7-h. renal arteries ; set. 

 subclavian artery ; spl. splenic artery ; syst. tr. systemic 

 trunk ; spm. spermatic artery ; ts. testis ; v. ventricle ; 

 vert, vertebral artery. 



