THE HUMAN BODY. 



moist serous membranes. That lining the dorsal cavity 

 is the arachnoid ; that lining the chest the pleura ; that 



lining the abdomen the perito- 

 neum ; the abdominal cavity is in 

 consequence often called the per- 

 itoneal cavity. Externally the 

 walls of these cavities are covered 

 by the skin, which consists of two 

 layers : an outer horny layer called 

 the epidermis, which is constantly 

 being shed on the surface and re- 

 newed from below ; and a deeper 

 layer, called the derm is and con- 

 taining blood, which the epider- 

 mis does not. Between the skin 

 and the lining serous membranes 

 are bones, muscles (the lean of 

 meat), and a great number of 

 other structures which we shall 

 have to consider hereafter. All 

 cavities inside the body, as the 

 alimentary canal and the air pas- 

 sages, which open directly or indi- 

 rectly on the surface are lined by 

 soft and moist prolongations of 

 the skin known as mucous mem- 

 branes. In these the same two 



FIG. 2. Diagrammatic longi . 



tudinal section of the body, a, laVCl'S are found as 111 the SK111, 

 the neural tube, with its upper -, ^ , ,-, r -i i i -n 



but the superficial bloodless one 

 is called epithelium and the deep- 

 er one the corium. 



Diagrammatically we may rep- 

 resent the human Body in longi- 



enlargement in the skull cavity 

 at a'; N. the spinal cord; JV', 

 the brain: ee. vertebrae form- 

 ing the solid partition between 

 the dorsal and ventral cavities; 



ber, opening behind into the 

 pharynx, from which one tube 

 leads to the lungs, I. and another 

 to the stomach,/; h, the heart; 

 fc, a kidney; s, the sympathetic 

 nervous chain. From the stom- 

 ach, /, the intestinal tube leads 

 through the abdominal cavity to 

 " the ali- 



aa' is the dorsal or neural cavity, 

 and b and c, respectively, the 

 thoracic and abdominal subdivi- 

 sions of the ventral cavity; d rep- 

 resents the diaphragm separating 



