458 APPLIED BIOLOGY 



(L) The best way to study the human skeleton is to compare a 

 mounted skeleton with labeled drawings in textbooks of anatomy 

 and physiology. At the same time the pupil should locate the posi- 

 tion of the larger bones in his own body. If a mounted skeleton is 

 not owned by the school, the pupil should locate as nearly as possible 

 the bones in his own body, using labeled pictures as a guide. The 

 names of the large bones are so frequently referred to that it is desir- 

 able to memorize them. Pupils who are studying drawing will 

 find various parts of the skeleton good objects for sketching ; but 

 as a rule this work is not possible in the limited time available for the 

 biology class-work. 



The most important parts to notice while examining a skeleton 

 are : (1) The backbone or vertebral column, to which all other parts 

 of the skeleton are attached. It is the central supporting axis of 

 the body. (2) The bones of the two pairs of limbs, comparing the 

 anterior with the posterior pairs. (3) The ribs and the bones which 

 connect the arms with the backbone. (4) The pelvis, which con- 

 nects the legs with the backbone. (5) The larger bones of the skull. 



372. Body-wall and Body-cavity. As in the frog, the 

 outer, fleshy wall which incloses the internal organs is the 

 body-wall; the internal cavity is the body-cavity. In the frog 

 there is one cavity in which lie the heart, lungs, liver, 

 stomach, intestine, kidneys, and reproductive organs. In 

 the human body the diaphragm forms a partition across 

 the body-cavity, dividing it into the anterior (upper) cavity 

 containing the heart and lungs and known as the thoracic 

 cavity (chest-cavity), and the posterior (lower) abdominal 

 cavity, which contains all the internal organs except the 

 heart and lungs. The thoracic cavity is inclosed by the 

 ribs, while the abdominal cavity is bounded by the muscular 

 walls of the abdomen. 



Structure of the Body-wall. (D) This is essentially the same in 

 man and other mammals, and so we may study any of the ani- 

 mals found in meat-markets. A slice of bacon will serve our pur- 

 pose. On the one edge of the slice is the skin or "rind." This, 

 of course, was the outside skin of the pig. The streaks of lean 

 meat are muscles of the body-wall. Fat has been deposited between 

 the muscles, and also between the muscles and the skin. The thick- 



