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A TEXTBOOK OF PHYSIOLOGY 



place. The intermediate part is closely adherent to the wall of the 

 posterior lobe ; its cells are clear, and tend to form colloid ; the anterior 

 portion is formed of columns of granular cells separated by blood- 

 channels (Fig. 258). 



Tne posterior lobe, or infundibuluin, is nervous in origin. It is 

 an imagination of the portion of the developing brain known as 

 the thalamencephalon. In some animals, such as the cat, it retains 

 its central cavity; in others this becomes entirely obliterated. Early 

 in development it becomes closely associated with cells of the pars 

 intermedia, so that eventually the posterior lobe becomes a com- 

 posite structure of intermediary and nervous epithelia a mass of 

 gland cells, neuroglial cells, and nerve fibres (Fig. 259). 



FIG. 260. RECORD OF BLOOD-PRESSURE AND MILK-FLOW rs DROPS FROM ONE NIPPLE 

 OF A LACTATING CAT. (Dixon.) 



At A pituitary extract was injected. 



The Functions of the Pituitary Body. The chief evidence of the 

 physiological action of the pituitary gland is obtained from clinical 

 experience and pathological findings, and from observations upon 

 the effects which follow injection or feeding extracts of the gland. 

 Owing to its anatomical position, it is difficult to obtain satisfactory 

 evidence by means of extirpation. It has been claimed that the 

 removal of the gland invariably causes death, often in thirty-six hours. 

 Many such deaths are undoubtedly due to post-operative shock. 

 Recently, skilled experimenters have succeeded in keeping animals 

 alive several months after removal of the pituitary. The effects 

 claimed to result from its removal are thus contradictory. 



The injection of extract of the anterior lobe is without physiological 

 action. Injection of extract of the intermediary and posterior lobe 



