CHAPTER XV 



THE FROG-HEART 



MAKE a special dissection of the upper part of the body of a large frog to show 

 the situation and connexions of the heart, its several cavities and the blood- 

 vessels leading to and from it. It is advantageous to distend the cavities with 

 gelatin solution and allow this to set. Notice a small nerve entering it on each 

 side along the superior vena cava ; this is the cardiac nerve, and is given off 

 from the vagus ; it contains also fibres from the sympathetic which reach the 

 vagus near the skull. Cut out a piece of the interauricular septum ; place 

 it in dilute methylene blue for five minutes ; wash with water, and examine 

 in water under the microscope for nerve fibres and groups of nerve cells. The 

 dissection of the heart may be made beforehand and kept for reference in dilute 

 formalin. 



Examine the contracting heart of a frog the brain and spinal cord 

 of which have been destroyed ; cut away the sternum and ensiform 

 cartilage and the front of the pericardium. Very gently raise the 



Common carotid. 



Right auricle. 

 Aortic bulb. 



Ventricle. 



Aorta. 



Pulmuno-cutaneous artery. 

 Left auricle. 



Aortic trunk. 

 Coronary sulcus. 



FIG. 55. HEART OP FROG : VENTRAL ASPECT (GAUPP). 



tip of the ventricle with a blunt instrument, and sever the peri- 

 cardial ligament which binds the ventricle to the back of the peri- 

 cardium. Do not grasp the heart with forceps or injure it in any way 

 by manipulation. 



On raising the ventricle the sinus venosus comes into view, 



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