86 THE STRUCTURE OF THE FOWL 



Organs associated with the 

 Circulatory System 



The body contains several organs which, 

 though not strictly a part of the circulatory 

 system, are so intimately connected therewith 

 as to justify a short description of them in 

 this place. One of these organs, the spleen, 

 may be regarded as interpolated in the path 

 of the blood-stream between the splenic artery 

 and the splenic vein. Other organs, such as 

 the thyroid and adrenal, may be looked upon 

 as glands without ducts for the transference of 

 the material they elaborate to a free surface. 

 This heterogeneous group of structures, fre- 

 quently designated the ductless glands, have 

 this feature in common : they discharge the 

 products of their activity directly into the 

 vascular system. Some of them produce sub- 

 stances known as hormones, which are capable 

 of producing marked effects upon the metabolic 

 or nutritive processes of the body. 



The spleen (Fig. 15) lies immediately to the 

 right of the junction of the glandular and mus- 

 cular stomachs. In colour it is reddish brown, 

 and in form it is generally rounded. Under the 

 peritoneum, which forms a thin serous invest- 



