THE CHEST AND ABDOMEN 6l 



it is completely separated from the lower portion by d partition which is partly 

 fleshy or muscular, and partly tendinous. In a small rabbit, for instance, the 

 central portion is tendinous, and so thin that it is transparent ; while round its 

 edges it is muscular. 



Thus we see that the great body cavity is divided into two 

 distinct parts by a muscular and tendinous partition. The 

 upper part of this cavity is called the thorax or chest ; the 

 lower portion is called the abdomen or belly ; and the arched 

 partition which separates these is called the diaphragm (Gr. dia, 

 across ; and phragma, a fence), also known as the midriff. The 

 thick and fleshy portion of the diaphragm or midriff of the 

 ox is sold by trie butcher under the name of skirt steak, or beef 

 skirt. 



The abdomen (Lat. abdo, I hide) or lower portion of the great 

 cavity may now be opened in a similar manner to that described 

 above, without injuring the diaphragm. It will be noticed that 

 certain vessels pass through this partition, and these are attached 

 so firmly to it that the organs with which they are connected can- 

 not be removed without injury to it unless the vessels are cut 

 above and below. 



After removing the organs of the abdomen we notice that its 

 walls have no bony support excepting at the back, as they consist 

 of the abdominal muscles and fibrous tissue only. The arrange- 

 ment of these muscles is illustrated in fig. 49. We leave the study 

 of the organs of the great cavity for future lessons. 



SUMMARY. 



8h HA \ Conical, with the diaphragm 



(' t as its base. 

 , Back Vertebral column. 

 Sides -f Ribs> 

 _. ,, t Intercostal muscles. 



Walls ' ' "L , Sternum. 



-t Costal cartilages. 

 V Floor Diaphragm. 



( A muscular partition, dividing the thorax 

 Diaphragm . ' from the abdomen. Convex above and 

 ( concave below. 



/ Roof Diaphragm 



Abdomen. . Walls . . , Sides and Front _ Abdo . 



Back Vertebral column, 

 des and Fron 

 minal muscles. 



QUESTIONS ON LESSON X. 



1. Describe the general structure of the body of a vertebrate animal. 



2. Where is the thorax ? What are the structures which surround it ? 



3. How would you proceed in order to examine the diaphragm of a small 



animal ? 



