RAN A. 345 



down the oviducts, where they receive a coat of albumen 

 and accumulate in the uterine part. 



If the urogenital organs and the anterior 

 lar°° Arterial venous system be now carefully removed the 

 arterial system can be completely exposed. 

 The heart is three-chambered, consisting of a ventricle 

 and two auricles. The right auricle receives venous blood 

 from the sinus venosus and the left auricle receives arterial 

 blood from the pulmonary veins. Both auricles, on con- 

 traction, drive their contents through valves into the 

 ventricle. From the ventricle there runs forwards between 

 the auricles a truncus arteriosus which first diverges into two, 



Fig. 243.' — Diagram of the TIiuncus Arteriosus 

 OF A Frog's Heart. 



Carotid. 



tlP^^!Xr~^^ Systemic. 

 /^^-^Atlv^^ Pulmonary. 



w 



and each of these divides into three, arterial arches. The 

 anterior, called the carotid arch^ passes up to a swollen 

 carotid gland and divides into a lingual and carotid artery 

 to the head. The second or systemic turns backwards, 

 gives off a brachial artery to the fore-limb, and meets its 

 fellow dorsally to the liver to form the single dorsal aorta. 

 The dorsal aorta gives off a large coeliaco-mesenteric to the 

 liver, stomach and other viscera, renals to the kidneys, and 

 eventually divides into two iliacs to the hind-legs. The 

 third arch, or pulmocuta?ieous^ divides into cutaneous to the 

 skin 2ixA pulmonary to the lungs. 



The truncus arteriosus has a long valve running up its lower part 

 which is arranged in such a way that certain portions of the blood pass 

 up certain arches. The auricles discharge venous and arterial blood 

 respectively into the ventricle, and in the ordinary way these would 



