58 LABORATORY WORK. 



Cut open the pericardium and study the heart. Its apex 

 is directed backward and to the (animal's) left; its broader 

 base in front and to the right. Tip the heart to your right, 

 and notice how the postcava enters it near the base on the 

 right side. Just before its entrance into the heart it 

 receives a similar vessel (the right precava) from in front, 

 while the left precava, passing behind the heart, enters it 

 from the side. Follow the precavaB forward, cutting 

 away the fatty-looking thymus gland just in front of the 

 heart in order to trace the vessel. Soon each divides into 

 a jugular vein (right and left) and a subclavian vein, the 

 former going forward in the neck, the latter into the fore 

 limbs. Trace the jugulars forward to head; do they 

 divide? Insert precavse and their branches as well as 

 anterior end of postcava in the sketch of the blood-vessels. 



Arising from the left side of the base of the heart is the 

 aortic arch. Follow this forward; to which side of the 

 body does it turn? From the arch of the aorta trace the 

 following vessels: (1) Right brachiocephalic artery, which 

 soon divides into the right subclavian artery and the right 

 common carotid artery. Follow the subclavian into the 

 limb, and the common carotid towards the head. Where 

 does the common carotid divide into internal and external 

 carotids ? (Just outside the common carotid will be found 

 a white thread-like nerve. It is the vagus (pneumogastric) 

 nerve, which supplies the stomach, heart, and lungs.) 

 (2) The left common carotid; and (3) close to it in its 

 point of origin from the aortic arch the left subclavian 

 artery. Trace these as before. Do you notice any differ- 

 ences between these vessels on the two sides of the body? 



Tip the heart to your left and trace the course of the 

 aorta from the origin of the left subclavian back to the 

 origin of the coeliac artery already found. On which side 



