CHAPTER XV 

 The Frog-Heart 



Dissection. Make a special dissection 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 the heart 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 



Common carotid. 



Aorta. 



Pulmono-cutaneous artery. 



Right auricle. f*^* $\ Left auricle ' 



Aortic bulb. -HL Mf T~ Aortictrunk - 



Coronary sulcus. 



Ventricle. 



FIG. 57. Heart of frog ; ventral aspect (Gaupp). 



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. 



Experiments. 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 tip of the ventricle with a blunt instrument, and sever the 

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



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