GROSS STEUCTUEE OF THE BODY 



29 



outside and forms what is called 

 an external skeleton, while in man 

 it is internal with the soft parts 

 packed upon it. If we examine a 

 diagram (Fig. 7) of the human 

 body split lengthwise the arrange- 

 ment of these soft and hard parts 

 is made clearer. Such a diagram 

 shows that the head is really a 

 box of bone resting on top of the 

 backbone with an external cover- 

 ing of soft parts, the eyes, ears, 

 cheeks, and scalp, and containing 

 within a mass of soft material 

 called the brain. This latter is 

 continued down the center of the 

 backbone in a long cord called the 

 spinal cord. The trunk is divided 

 into two cavities, one above the 

 other. The upper cavity, the 

 chest, is protected on each side 

 by arches of bone called the ribs, 

 on the front by the breastbone, 

 and is separated from the lower 

 cavity by a thin membrane called 

 the diaphragm. The lower cavity 

 is supported at the base by a 

 broad basket of bones called the 

 pelvis and at the back by the back- 

 bone. The upper cavity is filled 

 with the heart and lungs, while the lower contains a number 

 of soft organs (stomach, intestines, kidneys, etc.) . AVhen 



Fig. 7 — Diagram of a human 

 trunk split lengthwise ; a, 

 brain and cord cavity ; ft, 

 nasal cavity : c, mouth cav- 

 ity ; d, regions of alimentary 

 canal ; e, heart in chest cav- 

 ity or thorax ; /, partition 

 (diaphragm) separating the 

 chest cavity from the abdom- 

 inal cavity below. 



