190 THE NATURE STUDY COURSE. 



Aids from the Butcher. — The best practical way to convey 

 concepts of the internal organs is from specimens which may 

 be obtained from the butcher. The lungs and trachea, the 

 liver and pancreas of a sheep, the heart of the same animal 

 with its surrounding sac and two or three inches of the large 

 vessels left attached are far more effective aids in teaching the 

 analogous human organs than the best pictures ever made. 

 On request, a butcher will saw a sheep's skull and carefully 

 remove the brain with a few inches of the spinal cord ; and he 

 will think it little trouble to cut out its shin bone, saw it 

 across, and saw the upper half lengthwise through the cavity 

 and joint. He can easily supply you with specimens of joints 

 and tendons and muscles. With the aid of a good lens you 

 can show the openings of the little glands that secrete the 

 gastric juice in a bit of the wall of a pig's stomach. Using a 

 bicycle pump you can illustrate the expansibility of the lungs. 

 Obtain specimens of the different kinds of teeth from the 

 butcher or from the dentist or both. Break one of them with 

 a hammer to show the nerve paths in the roots and the pulp- 

 cavity ; reduce another on the grindstone lengthwise to show 

 cement, enamel, dentine and pulp-cavity, and grind a third 

 transversely to show a cross-section of these layers and parts. 



The Smaller Animals. — In teaching lessons on the cat and 

 dog, rabbit and guinea-pig, frog and bird, make numerous 

 comparative references to the human body. The child's lower 

 jaw, for example, admits of movement in three directions ; the 

 dog's moves up and down only ; the squirrel's or rat's moves 

 vertically and forward and backward ; while the sheep's has a 

 vertical and a wide sideways movement. With specimens of 

 the proper parts of these different types to study, the pupils 

 will discover that the molars of the dog and other carnivores 

 act like scissors, and the lower jaw is attached to the skull by 

 a simple hinge-joint ; the molars of the gnawers are grooved 

 from front to back, and the jaw slides in a groove in the base 



