l86 , VERTEBRATES 



it? What auricle receives it? Through how many open- 

 ings? This is a double circulation. Are there any mark- 

 ings on the outside of the heart which show the boundaries 

 of the ventricles ? Cut the heart through from right to left, 

 severing the auricles and ventricles. Note the openings be- 

 tween the auricles and ventricles. When the blood comes 

 into the left auricle, what hinders it from running into the 

 left ventricle if it be expanded? When the ventricle con- 

 tracts, what hinders the blood from going back into the 

 auricle? Look just below the auricle to find some valves 

 which are forced together in the contraction of the ventricle 

 and prevent this. Notice how they are anchored to the 

 walls of the ventricle. These are called the mitral, or bi- 

 cuspid valves. In like manner the valves on the right side 

 are called tricuspid valves. Can you give a reason for the 

 names? With a probe find where the blood leaves each of 

 the ventricles through the arteries ? The blood goes rapidly 

 through the body and the temperature is eight or ten degrees 

 higher than in any other animal. The heat is made in the 

 capillaries, where the oxj^gen is used in burning up waste 

 tissue. Explain the process. 



Draw the heart thus exposed (X2). 



Make an outline of the different systems and organs in the 

 visceral cavity. 



III. The Skeleton. — (i) The skeleton may now be 

 stripped of all the flesh so that the bones may be studied. 



(2) The shoulder girdle has already been found. Re- 

 move the last remaining bone, the scapula, with the wing. 

 Place it beside the coracoid and clavicle already removed 

 to see how the girdle is made to support the wing. Observe 

 the wing bone, the humerus, its shape, length, attachment 



