APPENDIX. 211 



blood returns to the right auricle of the heart hy the 

 venae cavas of a dark purple-red color. This color it 

 keeps until it reaches the lungs, where the reduced haemo- 

 globin becomes again oxidized. The bright red blood, 

 rich in oxygen and poor in carbon dioxide, is known as 

 "arterial blood," and the dark red as "venous blood;" 

 and it must be borne in mind that the terms have this 

 peculiar technical meaning, and that the pulmonary veins 

 contain arterial blood, and the pulmonary arteries contain 

 venous blood. The change from arterial to venous takes 

 place in the systemic capillaries, and from venous to 

 arterial in the pulmonary capillaries. 



What color is the blood when returned to the right auricle? Why? 

 What is meant by arterial blood? By venous? What veins contain 

 arterial blood? What arteries venous? Where does the change 

 from arterial to venous occur? Where that from venous to arterial? 



APPENDIX TO CHAPTER XIV. 



1. In the following directions " dorsal " means the side of the heart 

 naturally turned towards the vertebral column, "ventral" the side 

 next the breast-bone; "right" and "left" refer to the proper right 

 and left of the heart when in its natural position in the body; " an- 

 terior" means more towards the head in the natural position of the 

 parts; and "posterior" the part turned away from the head. 



2. Get your butcher to obtain for you a sheep's heart, not cut out 

 of the bag (pericardium), and still connected with the lungs. Impress 

 upon him that no hole must be punctured in the heart, such as is 

 usually made when a slaughtered sheep is cut up for market. 



3. Place the heart and lungs on their dorsal sides on a table in 

 their normal relative positions, and with the windpipe directed away 

 from you. Note the loose bag (pericardium) in which the heart lies, 

 and the piece of midriff (diaphragm) which usually is found attached 

 to its posterior end. 



4. Carefully dissecting away adherent fat, etc., trace the vessels 



