A FEW HINTS FOR TEACHERS. 47 



stand, must be exactly equal to the contraction of its 



antagonist on the opposite side of the joint, we easily 

 see why it takes some time to learn to stand. 



APPENDIX TO CHAPTER IV. 



Many of the facts described in this chapter can be exhibited to a 

 class with little trouble or expense. 



1. The sutures may be well seen on the skull of a rabbit or sheep. 

 All that is necessary is to boil it thoroughly and then pick the bones 

 clean, and wash out the brain. 



2. The structure of joints is easily exhibited on the fresh foot of a 

 sheep or calf. On cutting open the joints the tough ligaments around 

 them will be seen. The slippery synovial liquid covering the inside 

 of the joint can be felt by the finger. The smooth gristle will be 

 found to form a layer over the bones within the joint. A thin slice 

 of it may be readily cut off with a knife, and its translucency, flexi- 

 bility, and springiness exhibited. 



3. An example of a ball-and-socket joint may be easily obtained by 

 cleaning the thigh- and hip-bones of a rabbit or chicken. 



4. For a good example of a hinge-joint the most easily available 

 object is the skull of a dead cat. In this animal the lower jaw forms 

 a perfect hinge-joint with the rest of the skull. 



5. The pivot- joint between atlas and axis can be demonstrated on 

 the bones of a sheep's head and neck, after the piece of meat has 

 done its duty at table. For this purpose buy mutton. The odon- 

 toid process of a lamb is apt to separate. 



6. The form and structure of muscles can readily be exhibited on 

 the hind leg of a frog. Place the animal for a few minutes in a cov- 

 ered jar containing a pint of water to which has been added a tea- 

 spoonful of ether. When the creature has become quite unconscious 

 take it out, cut off its head, and run a stout pin down its back-bone 

 to destroy the spinal cord. In this way all chance of giving pain is 

 avoided. Then divide the skin at the top of each leg and pull it off. 

 Point out especially the muscles between knee- and ankle-joints, and 

 their long white tendons, many of them running to the toes. 



The leg of a chicken or turkey also affords an excellent object for 

 examining tendons. The bellies of most of the muscles which move 

 the toes lie in the part of the leg known as the "drumstick." Their 

 tendons run down the shank, and, if the skin be dissected off this, 

 are readily found. Pulling some of the tendons bends the toes, pull- 

 ing others straightens them; just as when they were pulled during 

 life by the contracting bellies of the muscles in the drumstick. 



7. The nerve of a muscle can be easily shown on the calf-muscle 

 of a frog's leg. Cut the tendon (tendo AchiHis) which attaches this 

 muscle to the heel. Then turn the muscle up, so as to expose its 

 under side. Its nerve will be seen, as a slender white thread, enter- 

 ing its deeper side a little way below the knee. 



