LYMPHATIC SYSTEM AND DUCTLESS GLANDS. 359 



thymus essentially consists of adenoid tissue, and is well sup- 

 plied with blood-vessels and lymphatics. 



The Pituitary Body (Fig. 75) is in part an offshoot of the 

 brain, and probably that portion of it is, like the pineal body, 

 a remnant of a once functionally important ancestral organ. 

 The anterior lobe of the pituitary body, however, is derived 

 in development from the pharynx, of which it is an embryonic 

 outgrowth. This part of it somewhat resembles the thyroid 

 in structure. Complete removal of the pituitary body in the 

 case of cats and dogs causes a lowering of temperature, mus- 

 cular twitchings and spasms, difficulty in breathing, general 

 lassitude, and death within a fortnight. These symptoms 

 improve when extract of the gland is injected. The.prgan 

 has therefore been supposed to form an internal secretion use- 

 ful in maintaining the nutrition of the muscular and nervous 

 systems. Disease of the pituitary body in man has been found 

 to be associated with the curious condition named acromegaly, 

 in which there is hypertrophy of the bones of the limbs and 

 face, and of parts of the skin and mucous membranes. In- 

 jection of the extract of the gland causes, in a normal animal, 

 a more powerful but not quicker heart-beat, and constriction 

 of the arteries. 



The Suprarenal Capsules or Adrenals are a pair of 

 small organs, weighing together about 12 grams (f oz.) placed 

 one on the top of each kidney. They have, however, no inti- 

 mate connection with the kidneys, and in many animals are 

 placed at some distance from them. Each consists of a denser 

 less colored external cortex, and a central deep yellow-brown 

 softer medulla. The cortex is subdivided into chambers by 

 connective tissue, and the chambers are filled by closely 

 packed, polygonal nucleated cells. Similar cells are found 

 in the medulla, which is, moreover, closely connected with 

 the sympathetic system and is richly supplied with nerves. 



It was noticed some fifty years ago by a physician named 

 Addisonthat certain obscure diseased conditions characterized 

 by great debility and by the appearance of bronzed patches 

 on the skin, and leading to death, were found on post-mortem 

 examination to be accompanied by disease of the adrenals. 

 The disease has hence been named Addison's disease. When 

 the suprarenal capsules are completely removed from animals 

 a similar fatal diseased condition results, death taking place 

 in warm-blooded animals within two or three days, and be- 



