PITUITARY BODY AND PINEAL GLAND 389 



from the internal mammary artery, a few coming from the inferior 

 thyroid, with occasional branches from the superior diaphragmatic or 

 the pericardial. They pass between the lobules, surround and penetrate 

 the vesicles and form a capillary plexus in their interior. The vesicles 

 in this respect bear a certain resemblance to the closed follicles of the 

 intestine. The veins are abundant, but they do not follow the course of 

 the arteries. The principal vein emerges at about the centre of the 

 gland posteriorly and empties into the left brachio-cephalic. Other small 

 veins empty into the internal mammary, the superior diaphragmatic 

 and the pericardial. A few nervous filaments from the sympathetic 

 surround the principal thymic artery and penetrate the gland. Their 

 ultimate distribution is uncertain. The lymphatics are very abundant. 



As regards chemical constitution, it may be stated in general terms 

 that the thymus contains matters of about the same character as those 

 found in the other ductless glands. 



Inasmuch as the thymus is peculiar to early life, the most important 

 points in its anatomical history relate to its mode of development. This, 

 however, does not present any great physiological interest and is fully 

 treated of in works on anatomy. 



Little that is definite can be said in regard to the physiology of 

 the thymus. In some recent experiments on Guinea pigs (Paton 

 and Goodall, 1904) it was found that removal of the thymus soon 

 after birth was not followed by any marked effects on the growth of the 

 animals ; but it seemed to diminish the resistance to the toxins of 

 staphylococci and streptococci. The operation had no effect on the 

 resistance to diphtheria. Later observations by Henderson showed that 

 "castration in cattle causes a persistent growth and a retarded atrophy 

 of the thymus gland " ; and a similar effect was noted in Guinea pigs 

 and rabbits. " In bulls and unspayed heifers the normal atrophy of 

 the thymus which begins after the period of puberty is greatly accel- 

 erated when the bulls have been used for breeding and when the 

 heifers have been pregnant for several months." The exact signifi- 

 cance of these experimental results is not apparent. 



PITUITARY BODY AND PINEAL GLAND 



These little bodies, situated at the base of the brain, are quite vas- 

 cular, contain closed vesicles and but few nervous elements and are 

 sometimes classed with the ductless glands. Physiologists have no 

 definite idea of their uses. 



The pituitary body, sometimes called the hypophysis, is of an ovoid 

 form, a reddish gray color, weighs five to ten grains (0.324 to 0.648 



