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A TEXTBOOK OF PHYSIOLOGY 



exhausted acini stain quite differently from islet tissue. By other 

 authorities the islets are looked upon as rudimentary pancreatic cells, 

 but the evidence for this cannot be considered satisfactory. 



The Function of the Thyroid and Parathyroids. The thyroid gland 

 lies in front of the trachea, and consists of two lobes, each about 

 2 inches long and 1 inch wide, joined by an isthmus. The para- 



Fio. 247. RECORD OF ARTERIAL PRESSURE AND INTESTINAL MOVEMENTS IN CAT. 



(Dixon.) 



At -4, 1 c.c. of 1 in 20,000 adrenalin was injected into a vein. The arterial pressure 

 rises, the intestinal movements arc inhibited, both effects corresponding to 

 stimulation of the sympathetic nerves. 



thyroids in mammals are small oval bodies 6 to 7 millimetres in length, 

 3 to 4 millimetres in breadth, 1-5 to 2 millimetres in thickness. They 

 are usually stated to te four in number, and varying in position in 

 different species of animals. 



The thyroid develops as a median endodermal dowiigrowth from 

 the tongue; to this the lateral lobes from the fourth cleft are added. 

 A considerable portion of the adult lateral lobes are derived, however, 



