CHAPTER II. 



Nerve-muscle preparation. Pith a frog by 

 cutting through the spinal cord at the occipito- 

 atlantoid ligament and passing a blanket pin or 

 wire into the skull and down the cord. Notice 

 that the muscles of the trunk and limbs are thrown 

 into contraction when the cord is being destroyed. 

 Make a circular incision round the middle of the 

 trunk through the skin only, and strip off the skin 

 from both hind limbs. Lay the frog on its back on 

 the frog-plate, and open the abdomen and thorax 

 freely but carefully. Notice the viscera (Fig. 22) 

 heart and lungs, liver, stomach, intestines, ovaries 

 and oviducts or testes, bladder. Cut through the 

 lower end of the rectum and through its attached 

 mesentery. On raising it two elongated red bodies 

 the kidneys are seen at the back of the abdomen, 

 partly covering the nerves which are passing down 

 to the hind limbs. Remove the kidneys without 

 touching the nerves. Now hold the frog up by its 

 legs so that the viscera hang towards the head, and, 

 cutting through the middle of the vertebral column 

 with strong scissors, remove the fore part of the 

 trunk and the viscera. Lay the hind part on the 

 frog-plate, and note the several muscles which are 

 seen on the front and back of the lower limbs (Figs. 

 23, 24). The gastrocnemius is generally used for 



