loo Laboratory Guide in Zoology 



the cut skin, notice over the thorax the large and 

 powerful pectoral muscles which control the movement 

 of the wings. Which way do the muscle fibres 

 extend ? 



X. — Circulatory System. Cut through the pectoral mus- 



cles and soft breastbone (sternum), extending the 

 incision back through the abdominal walls, thus expos- 

 ing the viscera of the thorax and abdomen. In the 

 thorax see the heart. Lift it carefully and cut the 

 connective tissues in such a way as to enable you to 

 study the important blood-vessels. From the front 

 of the heart on the left see the large aorta which 

 comes from the left ventricle. Before turning back- 

 ward this gives off the innominate arteries — one to 

 the right and one to the left. Each innominate artery 

 in turn has three branches ; namely, a carotid, extend- 

 ing forward toward the head ; a brachial, extending to 

 the wings, and a pectoral, extending to the pectoral 

 muscles. The large aorta extending backward may be 

 studied a little later when the thoracic and abdominal 

 viscera are removed. On its course it gives off various 

 branches, — to the stomach, to the liver, and to the legs. 

 Find three good-sized veins which pass into the right 

 auricle, and the right and left pulmonary arteries 

 which go from the right ventricle to the lungs. 



XI. — Study the structure of the heart itself. By cutting 

 transversely across the lower end see whether the ven- 

 tricles are completely separated from each other. Now 

 make a longitudinal section and study the structure of 

 the valves that connect one chamber with another. 



XII. — Mount a drop of blood upon a glass slide, and 

 study the shape of the corpuscles as seen with a high 

 power of the microscope. Make drawings of them. 



