STRUCTURE OF THE HUMAN MECHANISM 13 



long intestine (20 to 25 ft.) from the comparatively short 

 median dorsal body wall (see Fig. 156). The great arteries 

 and veins lie in the mesentery near the dorsal body wall, 

 and branches are distributed from them to the intestine 

 within this expand- 

 ing membrane (see 

 Fig. 163). 



The kidneys do 

 not He movably sus- 

 pended in the ab- 

 dominal cavity, as do 

 the intestines, but 

 are large organs, one 

 on each side, situated 

 near the spinal column 

 and dorsal to the ab- 

 dominal cavity from 

 which they are sep- 

 arated by the peri- 

 toneum. Arteries 

 and veins are sup- 

 plied to them from 

 the large median 

 artery and the me- 

 dian vein already 

 referred to (aorta 



cava 



and vena 



Fig. 15), and these 



renal arteries and veins are 



likewise outside- the abdom- 



5. Diagrammatic vertical right- 

 to-left section of the right thorax 



A, muscles, ribs, etc., of the body wall ; 

 JB, pleura, lining the same ; C, the pleural 

 space or cavity ; D, the pleural covering 

 of the lung ; E, connective tissue of the 

 lung; F, alveoli of the lung; G, dia- 

 phragm ; H, trachea ; 7, right bronchus, 

 branching; K, the pericardial space in 

 which lies the heart. Note the division 

 of the lung into two lobes 



inal cavity. 



The relation of the other organs to the peritoneum is more 

 complicated, notably in the case of the liver ; but in all cases 

 the organs are inclosed, or wrapped, either in a fold of the 

 peritoneum, as is the kidney, or in a fold of the mesentery, 



