RANA. 348 
down the oviducts, where they receive a coat of albumen 
and accumulate in the uterine part. 
Bisoavaced If the urogenital organs and the anterior 
lar. Arterial, Venous system be now carefully removed the 
arterial system can be completely exposed. 
The Zeart is three-chambered, consisting of a ventricle 
and two auricles. The r7ght auricle receives venous blood 
from the sinus venosus and the /eft 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 ¢runcus arteriosus which first diverges into two, 
Fig. 243.—DIAGRAM OF THE TRUNCUS ARTERIOSUS 
OF A Froc’s HEART. 
2 _» Carotid. 
AE Systemic. 
A Pulmonary. 
*S 
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 “ngual and carotid artery 
to the head. The second or systemic turns backwards, 
gives off a brachial artery to the forelimb, and meets its 
fellow dorsally to the liver to form the single dorsal aorta. 
The dorsal aorta gives off a large celiaco-mesenteric to the 
liver, stomach and other viscera, veza/s to the kidneys, and 
eventually divides into two zH#acs to the hind-legs. The 
third arch, or pudmocutaneous, divides into cutaneous to the 
skin and pu/monary to the lungs. 
The ¢runcus 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 
