RESPIEATOEY ORGANS. 



303 



the internal structures. The chief parts of this visceral peri- 

 toneum are the great omentum (Ge), the hepato-gastric liga- 

 ment (L), the mesentery {M), and the meso-colic mesentery. 

 The omentum is the large fold that connects the stomach with 

 the small intestine (3), and is often laden with fat ; the hepato- 



Pm. 158. — Theobetical, Losoitddinal, and Median Section of Abdominal 

 Cavity, to show Pekitoneum. 



1, Liver ; 2, stomach ; 3, small intestine ; 4, origin of floating colon ; 5, rectum ; 6, 

 vagina and uterus ; 7, bladder ; 9, posterior aoi-ta ; 10, diaphragm ; 11, post vena cava ; 

 12, inferior abdominal wall ; Pj), Pp, parietal peritoneum ; Pv, Pv, visceral peritoneum ; 

 Ir, hepato-gastric ligament ; M, mesentery ; Ge, great omentum. (Chauveau.) 



gastric ligament joins the liver to the stomach; the mesen- 

 tery supports the colon, and may also contain adipose tissue. 

 Eectum (5), vagina (6), and the hladder (7) are also surrounded 

 by it. 



Situated in the thoracic cavity we shall note two important 

 structures — namely, the lungs and heart (fig. 157, Lu and H). 

 The respiratory organs are absolutely necessary for the main- 

 tenance of life, for life requires not only the absorption and 

 assimilation of nutritive matters, but also oxygen from the air 

 to enter into the circulation of these matters. In animals with 

 red blood this element in mixing with the nutritive fluid com- 

 mences by expelling COj, and communicates to that fluid its 

 bright red colour. This produces the combustion that partly 



