APARTMENTS AND FURNITURE. 177 



substance we swallow, and the motion of swal- 

 lowing, press it down and close it tightly. 

 And it is well that it is so ; for if it were not, 

 the substances which we swallow would often 

 drop into the passage to which this trap door 

 opens, and cause us great trouble. 



THE CHEST. Beyond the door, the pas- 

 sage greatly enlarges, and proceeds downwards 

 into the chest, the large apartment which I have 

 just mentioned. This apartment is one of the 

 largest in the house I live in, and nearly fills 

 the upper story. It is one of the kind which 

 has no outer doors, neither is it connected with 

 any other cavity or apartment. It is supported 

 on all sides by strong bony walls ; the breast 

 bone in front, the back bone behind, and the 

 ribs at the sides. Above, at the fore part of the 

 neck, it is of course less guarded with bone ; 

 and at the bottom there are no bones at all. It 

 is separated from the apartments of the second 

 or lower story, by a strong skin or membrane 

 called the diaphragm or midriff. 



CAVITY OF THE LUNGS. The trap door, of 

 which I have spoken, does not lead directly into 



