150 PHYSIOLOGY OF FARM ANIMALS [CH. XI. 



Beyond these facts nothing can be stated definitely regarding 

 its utility to the organism, but according to some authorities it 

 is also a factory for erythrocytes. 



The Thymus. This organ is composed of lymphoid tissue 

 closely packed in the cortex but less dense in the medulla. The 

 latter contains the concentric corpuscles of Hassal which are 

 epithelial cells arranged in rings and are specially characteristic 

 of the thymus. Their significance is unknown. The organ is 

 usually situated on the ventral surface of the great vessels com- 

 municating with the heart, but in some animals (e.g. guinea-pigs) 

 the thymus bodies are placed much further forward in the neck. 

 The thymus normally atrophies about the age of puberty. Its 

 functions are very obscure, and its removal appears to be followed 

 by no harmful results. It seems probable however that after 

 extirpation the functions of the thymus are taken over by other 

 lymphatic glands. 



