PART II. 



MICROSCOPIC ANATOMY OF THE ORGANS. 



IN this section we have to deal with the structure of organs 

 which are built up of the tissues which have been studied. 

 Some of these organs, it will be seen, are made up of all the 

 different tissues, while others are much more simple. A fea- 

 ture to which special attention will be directed is the unitary 

 structure of many of the organs. In other words, the tissues 

 are grouped together into units, which are repeated many times 

 to form the whole organ. These may be secretory, excretory, 

 or circulatory units. 



The organs will be treated in the following order : 



I. Circulatory system. 

 II. Alimentary system. 



III. Respiratory system. 



IV. Urinary system. 



V. Reproductive system (sexual organs). 

 VI. Motor system : 



1. Skeletal system. 



2. Muscular system. 



VII. Nervous system and sense organs. 



I. CIRCULATORY SYSTEM. 



Under this heading it is necessary to take up the heart, 

 blood-vessels, lymph-vessels, and blood-forming organs i. e., 

 the lymph glands, spleen, thymus, bone-marrow, and those 

 ductless glands whose internal secretion is poured into the cir- 

 culatory system and exercises on it a profound influence i. e., 

 the thyroid, adrenal, pituitary body, and carotid gland. 



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