LEPUS. 387 
is more passive. The elastic lungs contract, the ribs fall 
and the diaphragm rises. 
Anterior to the heart and lying over the great blood-vessels 
is the ¢hymus, a ductless gland which must be removed to 
expose the blood-vessels. 
The ear? is four-chambered, as in the pigeon, and is but 
slightly larger. It differs but little from that of 
the latter. The three auriculo-ventricular valves 
on the right side are called ¢rvicuspid valves and 
the two on the left side are called the mtral valves. 
The venous system, as in the two last types, has definite 
vessels or veins and consists of three parts. We have 
already noticed the epaticportal system. The pulmonary 
system consists of two pulmonary veins leading from the 
lungs and opening directly into the left auricle. The 
systemic system consists of three main veins opening into 
the vight auricle. Two are paired and anterior, and are 
known as the fprecavals, and the third is posterior and 
median, known as the postcaval. 
The venous blood from the superficial part of the head 
is removed by the anterior and postertor facial veins which 
unite behind the mandible to form the external jugular 
vein. This passes down the neck, at the base of which it 
receives a small znéernal jugular coming from the brain and 
a vertebral, It then unites with the subclavian, a large 
vein mainly formed of a continuation of the brachial vein 
(of the fore-limb), and the two form the precaval which 
passes into the thoracic cavity in front of the ribs.* The 
right precaval only has an azygos vein passing backwards 
beside the vertebral column and said to be a vestige of the 
right cardinal vein of lower types.t 
The postcaval can be traced backwards through the 
diaphragm. It commences in the pelvic region by the 
union of two internal tliacs, and then receives two femorals 
from the legs, two 2//0-/umbars from the back, genztals, renals, 
dorso-lumbars, hepatics and phrenics from the genital organs, 
kidneys, dorsal muscles, liver and diaphragm respectively. 
Blood- 
Vascular. 
* The skin has two cutaneous veins not unlike those of the frog in position. The 
anterior arises from the subclavian and the posterior from the femoral. Both are 
enormously distended in the female when the mammary glands are active. 
+ The thoracic wall is drained by two small veins, the axtertor intercostal and 
the internal mammary falling into the precaval on each side, 
