DISSECTION Off A RAT. 91 



responding fore limb. Trace the jugulars forward to head ; 

 do they divide ? Insert precava and its 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 

 aorta. Follow this forward; to which side of the body 

 does it turn ? From the arch which the aorta makes 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 and 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 differences 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, 

 (dorsal or ventral) of the oesophagus does the aorta pass ? 

 On which side is the heart ? Insert the vessels now made 

 out in the sketch, which should now represent the principal 

 vessels of the systemic circulation. 



Dissect the aortic arch loose from the surrounding tissue, 

 lift it up, and see dorsal to it the pulmonary arteries going 

 to the lungs. From what part of the heart do they arise ? 

 Tip the heart to the animal's right and see the pulmonary 

 veins, which bring the blood back from the lungs to the 

 heart. On which side, with reference to the pre- and post- 

 cava, do they enter the heart ? The pulmonary arteries 



