THE CHEST. 221 



lungs the BRONCHIAL TUBES. These trunks enter deeply into the substance 

 of the lungs. They presently subdivide, and the subdivision is continued in 

 every direction, until branches from the trachea penetrate every assignable por- 

 tion and part of the lungs. They are still air-passages, carrying on this fluid to 

 its destination, for the accomplishment of a vital purpose. 



They also continue exposed to pressure ; but it is pressure of a new kind, a 

 pressure alternately applied and removed. The lungs in which they are 

 embedded alternately contract and expand ; and these tubes must contract and 

 expand likewise. Embedded in the lungs, the cartilaginous ring of the bronchi 

 remains, but it is divided into five or six segments connected with each other. 

 The lungs being compressed, the segments overlap each other, and fold up and 

 occupy little space ; but the principle of elasticity is still at work ; and as the 

 pressure is removed, they start again, and resume their previous form and 

 calibre. It is a beautiful contrivance, and exquisitely adapted to the situation 

 in which these tubes are placed, and the functions they have to discharge. 



But we must pause a little and consider the structure and functions of the 

 chest. 



CHAPTER X. 

 THE CHEST. 



a The first rib. 



b The cartilages of the eleven hindermost, or false ribs, connected together, and uniting with 

 that of the seventh or last true rib. 



c The breast-bone. 



d The top, or point, of the withers, which are formed by the lengthened spinous, or upright 

 processes of the ten or eleven first bones of the back. The bones of the back are 

 eighteen in number. 



e The ribs, usually eighteen on each side ; the seven first united to the breast-bone by car- 

 tilage ; the cartilages of the remaining eleven united to each other, as at b. 



f That portion of the spine where the loins commence, and composed of five bones. 



g The hones forming the hip, or haunch, and into the hole at the bottom of which the head of 

 the thigh-bone is received. 



h The portion of the spine belonging to the haunch, and consisting of five pieces. 



t The bones of the tail, usually thirteen in number. 



THE chest, in the horizontal position in which it is placed in the cut, is of a 

 somewhat oval figure, with its extremities truncated. The spine is its roof ; 

 the sternum, or breast, its floor ; the ribs, its sides ; the trachea, oesophagus, 

 and great blood-vessels passing through its anterior extremity and the 



