LABORATORY MANUAL OF PHYSIOLOGY. 



By means of a V-shaped incision through the walls of each ven- 

 tricle, with the apex of the V toward the apex of the ventricle, open 

 the right and left ventricles. Note the openings between the auri- 

 cles and ventricles and between the ventricles and large arteries. 

 Note the shape and attachments of the auriculo- ventricular valves, 

 the chordae tendineae and papillary muscles. Compare these with 

 the valves guarding the openings of the large vessels, the semi- 

 lunar valves. Determine the direction of opening of the various 

 valves. 



XV. DISSECTION AND RELATIONS OF THE EXTRINSIC CARDIAC 



NERVES. 



This should first be done upon the dead animal. Make a median 

 incision in the neck of a rabbit, through the skin and superficial 

 fascia. Continue the incision down to the trachea, which is used as 

 a guide. Separate the muscles from either side of the trachea and 

 pull them to one side. Beneath the sterno-mastoid muscle the ca- 

 rotid artery and the large nerve trunks running along with it will 

 now be exposed. Immediately behind the artery lies the vagus 

 nerve trunk. This nerve contains, among a number of other fibres, 

 inhibitory fibres for the heart. A somewhat smaller nerve is seen 

 behind and to the inner side of the artery. This is the cervical 

 sympathetic. Next to this, in the rabbit, is a small nerve, the de- 

 pressor. Opposite the larynx, the superior laryngeal branch joins 

 the main vagus trunk. Here also the depressor nerve joins the su- 

 perior laryngeal and enters the main trunk with it or splits into two 

 branches, one joining the vagus and the other the superior laryn- 

 geal (see Fig. 31). 



XVI. DIRECT OBSERVATION OF THE PULSATING MAMMALIAN 



HEART. , 



Inject under the skin of a rabbit J grain of morphine sulphate. 

 Lightly anaesthetize with ether. Expose the trachea through a me- 

 dian incision in the neck. The rabbit should be tied, back down, 

 upon the rabbit-board, the fore limbs being brought down to the 



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