II PRACTICAL DIRECTIONS 31 



reproduction ; the muscles, organs of movement ; the brain 

 and spinal cord, together with the nerves, organs of control, 

 serving to direct or control the actions of the body ; the 

 skin, nose, eye, and ear, sensory organs, by which communi- 

 cations are kept up with the external world. 



Tissues. — Notice also that the various parts of the body 

 are built up of different materials, or tissues as they are 

 called. We have already distinguished muscle, bone, 

 cartilage, connective-tissue and nervous tissue. Other 

 tissues we shall meet with in the course of a more careful 

 examination. 



PRACTICAL DIRECTIONS. 



To kill a Frog for Dissection.— Place a frog on a plate, and cover 

 it with a tumbler, or put it into a stoppered bottle. Soak a little bit of 

 cotton-wool or sponge in chloroform, and push it under the edge of the 

 tumbler, or drop it into the bottle. In a few minutes the vapour will 

 make the animal quite insensible, and a somewhat longer exposure will 

 kill it painlessly. 



External Characters- — Observe the voluntary and the involuntary 

 respiratory movements of the living animal, and compare with a dead 

 frog when making out the external characters (pp. 4-8) and the position 

 of the various parts of the skeleton (p. 16). 



Sketch the entire animal from the side or from above. 



The Cavity of the Mouth. — Gently open the mouth of a dead 

 frog as wide as possible, and make out the points described on pp. 16 

 and 17. Sketch. 



The Body-wall. — Lay the frog on its back in the dissecting-dish, and 

 fix it firmly by sticking pins through the skin of the arms and legs. 

 With the forceps, held in the left hand, pinch up the skin of the 

 abdomen near the middle line between the thighs, and make a nick in it 

 with the points of the scissors. Then, holding the edge of the hole thus 

 made with the forceps, pass in a probe and push it forwards as far as it 

 will go without opposition. Note : — 



The sub-cutaneous lymph-sinuses, and the underlying muscle. 

 With the scissors extend the incision made in the skin of the belly 

 forwards, in a straight line, to the chin. Holding up the edge of the 



