572 THE DUCTLESS GLANDS ENDOCRIN GLANDS 



pends upon the adrenalin content of the granules. Adrenalin produces 

 a contraction of involuntary muscle. Its function appears to be to 

 maintain the proper tonus of the blood-vessels. 



VIII. HYPOPHYSIS CEREBRI 



(Pituitary Body) 



The HYPOPHYSIS is a gland of the internally secreting (endocrin) 

 or ductless type. The secretion passes directly from the specific cells 

 into capillaries. This gland is a composite structure, arising from the 

 association of two originally distinct anlages; one taking origin as a 

 median dorsal diverticulum (Rathke's pouch) from the primitive mouth, 

 the other as a medial ventral evagination from the second cerebral 

 vesicle (third ventricle) or diencephalon. Both components are thus 

 ectodermal. The cerebral flask-shaped element invaginates the buccal 

 element and modifies the original" bulbar shape of the latter into 

 that of a cup. The buccal connection disappears, while the cerebral 

 connection persists as the infundibular stalk of the definitive struc- 

 ture. 



The hypophysis is present as an essentially similar organ in all 

 craniates. In man it measures about 12 mm. in the transverse, about 

 7 mm. in the sagittal, and about 5 mm. in the vertical diameter. It 

 has an inverted mushroom shape, the stalk or infundibulum, a hollow 

 funnel-shaped structure lined with ependyma, attaching it to the brain, 

 while its head is lodged in the sella turcica of the skull. The hypo- 

 physis was known to the early anatomists as the pituitary gland (Vesal, 

 1553), and was supposed to function as an excretory organ in the elimi- 

 nation of mucus (pituita) from the brain by way of the nose. The 

 term pituitary gland is now generally applied only to the larger anterior 

 component or epithelial lobe; the posterior component or neural lobe 

 is designated the infundibular process; the term hypophysis is applied 

 to the associated elements. But hypophysis and pituitary body are still 

 often used synonymously. The neural and glandular tissues are said 

 to be connected with each other by means of nerve fibers, probably sym- 

 pathetic, connective tissue, and blood-vessels. Certain investigators have 

 described accessory pituitary bodies. Thus Haberfeld (1909) finds in 

 man at all ages a 'pharyngeal pituitary,' a solid cord of neutrophilic 

 cells about 5 mm. in length immediately behind the vomer. This is 

 frequently the initial seat of tumors. 



