PRACTICAL EXERCISES 



197 



by cutting through the pectoral girdle in the way described in 2 (p. 194). 

 On clearing away a little connective tissue and muscle with a seeker, 

 three large nerves will come into view. The upper is the glosso- 

 pharyngeal, the lower the hypoglossal; the vagus crosses diagonally 

 between them (Fig. 91). Above the vagus trunk, running parallel to 

 it, and separated from it 

 by a thin muscle and a 

 bloodvessel (the carotid 

 artery), lies its laryngeal 

 branch. The vagus should 

 be traced up to the gang- 

 lion situated on it near its 

 exit from the skull. 



(2) Then cut away the 

 lower jaw, dividing and 

 reflecting the membrane 

 covering the roof of the 

 mouth. At the junction 

 of the skull and the back- 

 bone will be seen on each 

 side the levator anguli 

 scapulae muscle (Fig. 92). 

 Remove this muscle care- 

 fully with fine forceps. 

 Clear away a little con- 

 nective tissue lying just 

 over the upper cervical 

 vertebrae, and the sym- 

 pathetic chain, with its 

 ganglia, will be seen. Pass 

 a fine silk thread beneath 

 the sympathetic about the 

 level of the large brachial 

 nerve, by means of a 

 sewing-needle which has 

 been slightly bent in a 

 flame and fastened in a 

 handle. Tie the ligature, 

 divide the sympathetic be- 

 low it, and isolate it care- 

 fully with fine scissors up 

 to its junction with the 

 vagus ganglion. 



Batteries To set up a 

 Daniett Cell. Fill the por- 

 ous pot (Fig. 230, p. 724), 

 previously well soaked in 

 water, with dilute sulph- 

 uric acid (i part of com- 

 mercial acid to 10 or 15 

 parts of water) to within 

 i inches of the brim, and place in it the piece of amalgamated zinc. If 

 the zinc is not properly amalgamated, leave it in the pot fo'r a minute or 

 two to clean its surface. Then lift it out, pour over it a little mercury, 

 and rub the mercury thoroughly over it with a cloth. Put the pot 

 into the outer vessel, which contains the copper plate, and is filled 

 with a saturated solution of sulphate of copper, with some undissolved 



B 



B 



Fig. 90. Arrangement for recording Auricular 

 and Ventricular Contractions (and studying the 

 Influence of Temperature of the Heart). C, 

 clamp holding the heart at the auriculo-ven- 

 tricular groove; P, pulley round which a thread 

 attached to the apex of the ventricle passes to 

 the lever L'; L, lever connected with auricle. 

 (The rest of the arrangement is for studying the 

 influence of temperature on the heart and its 

 nerves, G being a vessel filled with physiological 

 salt solution in which the heart is immersed; R, 

 an inflow tube from a reservoir containing salt 

 solution at the temperature required; O', an out- 

 flow tube by which G may be emptied into the 

 beaker B'; O, a tube passing to the beaker B to 

 prevent overflow from G; T, a thermometer.) 



