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 thymus^ a ductless gland which must be removed to 

 expose the blood-vessels. 



The heart is four-chambered, as in the pigeon, and is but 



slightly larger. It differs but little from that of 



Vasc-SSr ^^^ latter. The three auriculo-ventricular valves 



on the right side are called tricuspid valves and 



the two on the left side are called the mitral 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 hepatic-portal 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 right auricle. Two are paired and anterior, and are 

 known as the precavals, and the third is posterior and 

 median, known as \^^ postcaval. 



The venous blood from the superficial part of the head 

 is removed by the anterior and posterior 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 internal 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 iliacs^ and then receives two femorals 

 from the legs, two ilio-lumbars from the h2,(^^ genitals^ renals^ 

 dorso-lumbars, hepatics dcnd phrenics from the genital organs, 

 kidneys, dorsal muscles, liver and diaphragm respectively. 



* 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. 



t The thoracic wall is drained by two small veins, the anterior intercostal and 

 the internal mamjuary falling into the precaval on each side. 



