342 CHORDATA. 
lungs and the urinary bladder belong morphologically but 
not physiologically to the alimentary system. 
The Zeart lies ventrally to the cesophagus, enveloped in 
its pericardium. Its structure will be con- 
sidered later. The veins lie superficially to 
the arteries and consist of an anterior and 
a posterior system. The anterior system is paired; the 
posterior is in great part single. 
Anteriorly a small “gual vein from the tongue is seen 
to unite with a mandibular from the lower jaw to form the 
external jugular. This runs backwards to join with the 
large subclavian already seen, which runs along the anterior 
wall of the abdominal cavity. As already noticed, the sub- 
clavian is made up of the dvachial and the musculo-cutaneous. 
The area between external jugular and subclavian is drained 
by a small but deep vein, the zz#ominate, which is formed 
of the znternal jugular emerging from the brain and the sué- 
scapular from the dorsal region. The innominate joins the 
external jugular and subclavian, the three uniting to form 
the precaval vein, which passes backwards and inwards to 
fall into the s¢zus venosus dorsal to the heart. 
In the posterior system the portal vein can be seen 
coming from the stomach, spleen, pancreas and duodenum, 
and falling into the liver; it constitutes the Aepatic-portal 
system. Just before it enters the liver it receives the 
anterior abdominal vein-already noted. 
If the alimentary canal be now carefully removed by 
cutting through the rectum and through the cesophagus, 
the £idneys are exposed and the rest of the venous system 
is clearly distinguished (see Plate VI.). The /emora/veins are 
large veins leading up from the legs. Before entering the ab- 
dominal cavity each divides into a pelvic and a renal portal. 
The former comes up to meet its fellow and the two form the 
anterior abdominal to the liver. The renal portal proceeds 
forwards, receives a sciatic from the inner side of the leg, and 
breaks up along the outer border of the kidney; hence the 
frog has a well-developed renal-portal system as well as 
a hepatic-portal. The blood from the large hind-limbs 
must pass either through the kidney by the renal portal, or 
‘through the liver by the anterior abdominal before reaching 
the heart. Between the kidneys is a large postcaval which 
Blood-Vascu- 
lar. Venous, 
