4 TEXT-BOOK OF PHYSIOLOGY. 



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 determinate 

 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 muscle, the 

 nerve, and the tegumentary systems. 



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 

 accomplishment of some definite object, and to which the term physiologic 

 apparatus has been applied. While in the community of organs which 

 together constitute the animal body each one performs some definite function, 

 and the harmonious cooperation of all is necessary to the life of the individual, 

 everywhere it is found that two or more organs, though performing totally 

 distinct functions, are cooperating for the accomplishment of some larger 

 or compound 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 com- 

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

 vessels of the body, and especially those in relation to the villi of the small 

 intestine, constitute the absorptive apparatus, the function of which is the 

 introduction of new material into the blood. The heart and blood-vessels 

 constitute the circulatory apparatus, the function of which is the distribution 

 of blood to all portions of the body. The lungs and trachea, together with 

 the diaphragm and the walls of the chest, constitute the respiratory apparatus, 

 the function of which is the introduction of oxygen into the blood and the 

 elimination from it of carbon dioxid and other injurious products. The 

 kidneys, the ureters, and the bladder constitute the urinary apparatus. The 

 skin, with its sweat-glands, constitutes the perspiratory apparatus, the func- 

 tions of both being the excretion of waste products from the body. The 

 liver, the pancreas, the mammary glands, as well as other glands, each form 

 a secretory apparatus which elaborates some specific material necessary 

 to the nutrition of the individual. The functions of these different physio- 

 logic apparatus e.g., digestion, absorption of food, elaboration of blood, 

 circulation of blood, respiration, production of heat, secretion, and excretion 

 are classified as nutritive functions, and have for their final object the 

 preservation of the individual and therefore the species. 



