XIII 



PHYLUM CHORDATA 



279 



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. an.\ a ventricle (v.pt.'), 



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 right. 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, 9 32.-Rana temporaria. The arterial system, 



and its dorsal and Ven- 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 ; 

 ccel. mes. cosliaco-mesenteric artery ; cu. cutaneous 

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

 gastric artery ; hp. hepatic artery ; il. iliac artery ; 

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

 ly. lingual artery ; ln<j. lung ; ces. oesophageal artery ; 

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

 trunk ; r. au. right auricle ; rn. renal arteries ; scl. 

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

 trunk ; spin, spermatic artery ; is. testis ; v. 

 vert, vertebral artery. 



tral walls are raised up 

 into muscular ridges or 

 trabeculaB with inter- 

 stices between them. 

 The conus springs from 

 the right side of the 

 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 (/. v.~) which springs from its dorsal wall and is free 



s 2 



