THE PIGEON 175 



Exercise 11. Make a semidiagrammatic drawing of the ventral aspect 

 of the heart and the vessels just described. 



The Great Veins. Turn the apex of the heart forward and pin 

 it there ; carefully and thoroughly clean its dorsal surface. Iden- 

 tify the right and left auricles and the right and left ventricles. 

 Three large veins will be seen entering the right auricle: the 

 right and left precaval veins and the postcaval vein. If these 

 are not seen readily, the two precavals may be found by following 

 the large jugular veins, one of which is on each side of the neck, 

 posteriorly. The right precaval is a very short vein which enters 

 the right anterior border of the auricle. It is formed by the union 

 of three large veins, which meet just in front of the auricle: the 

 right brachial vein, which comes from the wing ; the right pectoral, 

 which comes from the pectoral muscles; and the right jugular 

 vein, which comes from the head. The pectoral vein receives at 

 its proximal end the internal mammary vein, which lies alongside 

 the mammary artery on the inner surface of the ribs. 



The left precaval will be seen passing across the dorsal surface 

 of the heart to the left side of the right auricle ; it is formed by 

 the union of the same veins as the right precaval. 



Free these veins from the tissues surrounding them. Trace the 

 jugular forward along the side of the neck, where it lies close to 

 the vagus, or pneumogastric, nerve and the cervical artery. Be- 

 neath the under surface of the skull the two jugulars are united 

 by a transverse vein. Note the veins from the thymus gland and 

 the crop which join the jugular, and note also the large vertebral 

 vein. This vein brings blood from the brain and lies in the verte- 

 brarterial canal together with the vertebral artery. 



The postcaval vein is a large vessel which enters the right auricle 

 directly from behind. It brings blood from the hinder part of the 

 body and passes through the right lobe of the liver to the heart. 



Turn the heart over to the animal's right and pin it there; 

 pull the heart gently forward and look for the pulmonary veins, 

 which bring blood from the lungs to the left auricle. Each is a 

 short, wide vein which will be seen to arise from the lung by sev- 

 eral roots and go directly to the left auricle. 



