XIIL] THE FROG. 743 



7. In front of the sciatic plexus lying on the muscles 

 bounding posteriorly the abdominal cavity are three 

 nerves running obliquely downwards and outwards on 

 each side: they are continuous with the 4th, 5th and 

 6th spinal roots. 



8. Sqme nerves of the neck. 



a. Pass a piece of tubing down the gullet so as to 

 distend it : and then carefully remove the mylo- 

 hyoid muscle (B. 6. a). 



b. Find the posterior cornu of the hyoid bone on 

 one side : from it a slip of muscle (petrohyoia) 

 will be seen passing up towards the occipital 

 region of the skull. Lying along the posterior 

 border of this muscle is the pneumogastric nerve; 

 follow its branch to the heart. 



c. Lying on the petrohyoid and in front of the 

 pneumogastric, from which it arises, is the laryn- 

 geal nerve. 



d. Some way in front of the laryngeal nerve is seen 

 the glossopharyngeal ?ierve, turning up towards 

 the front of the jaw. 



e. Superficial to the glossopharyngeal, but with a 

 generally similar direction, is the hypoglossal 

 ntrve (B. 6. a). 



9. The brachial nerve. 



Lay it bare in the arm-pit and follow it back to the 

 spinal cord : it is formed by the union of the 2nd and 

 3rd spinal nerves. 



10. The sympathetic system. 



a. Gently raise the aorta : along each side of it will 

 be found the main sympathetic trunk. A slender 



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