GENERAL STRUCTURE OF THE ANIMAL BODY. 5 



creas. In the posterior portion of the abdominal cavity are found the 

 kidneys, ureters, and bladder, and in the female the organs of reproduc- 

 tion. The thoracic and abdominal cavities are each lined by a thin 

 serous membrane, known, respectively, as the pleural and peritoneal 

 membranes, which, in addition, are reflected over the surfaces of the 

 organs contained within them. The alimentary canal and the various 

 cavities connected with it are lined throughout by a mucous membrane. 

 The surface of the body is covered by the skin. This is composed of an 

 inner portion, the derma, and an outer portion, the epidermis. The 

 former consists of fibers, blood-vessels, nerves, etc.; the latter of layers 

 of scales or cells. Embedded within the skin are numbers of glands, 

 which exude, in the different classes of animals, sweat, oily matter, etc. 

 Projecting from the surface of the skin are hairs, bristles, feathers, claws. 

 Beneath the skin are found muscles, bones, blood-vessels, nerves, etc. 



The appendicular portion of the body consists of two pairs of symmetric 

 limbs, which project from the sides of the trunk, and which bear a deter- 

 minate relation to the vertebral column. They consist fundamentally of bones 

 surrounded by muscles, blood-vessels, nerves and lymphatics. The limbs, 

 though having a common plan of organization, are modified in form and 

 adapted for prehension and locomotion in accordance with the needs of the 

 animal. 



Anatomic Systems. All the organs of the body which have certain 

 peculiarities of structure in common are classified by anatomists into systems 

 e. g., the bones, collectively, constitute the bony or osseous system; the 

 muscles, the nerves, the skin, constitute, respectively, the muscular, the ner- 

 vous, and the tegumentary system. 



Physiologic Apparatus. More important from a physiologic point of 

 view than a classification of organs based on similarities of structure is the 

 natural association of two or more organs acting together for the accomplish- 

 ment of some definite object, and to which the term physiologic apparatus 

 has been applied. While in the community of organs which together con- 

 stitute the animal body each one performs some definite function, and the 

 harmonious cooperation of all is necessary to the life of the individual, every- 

 where it is found that two or more organs though performing totally distinct 

 functions, are cooperating for the accomplishment of some larger or com- 

 pound function in which their individual functions are blended e. g., the 

 mouth, stomach, and intestines, with the glands connected with them, 

 constitute the digestive apparatus, the object or function of which is the 

 complete digestion of the food. The capillary blood-vessels and lymphatic 



