PAEAGANGLIA 



571 



others interpret them as modified rmlothelial cells of the blood-vessels. 

 Vincent suggests that this body may function as a 'safety-valve' in the 

 course of the peripheral circulation; he regards the balance of evidence 

 as against any function involving an internal secretion. 



VII. PARAGANGLIA 



Te 



The so-called chromaffiu system includes besides the medulla of 

 the suprarenal and the carotid gland, other larger and smaller groups 

 of chromaftin cells ('pheochrome organs') derived from embryonal sym- 

 pathetic cells and scattered along 

 the entire sympathetic nervous 

 system, the PAHAGAXGLIA. They 

 are therefore present in many 

 organs which receive a consider- 

 able sympathetic innervation, e.g., 

 kidney, liver, uterus, testis, etc. 

 Chromaffin tissue composed of 

 widely scattered cells is present 

 also in the sympathetic trunks, 

 particularly the various plexuses, 

 among the definitive neurons of 

 this system. 



The largest paraganglia (or- 

 gans of Zuckerkandl) occur in 

 close relation to the inferior mes- 

 enteric artery, one on either side. 

 Other smaller groups are found 

 in relation to the abdominal 

 aorta. Busachi has recently 

 (1912) described chromaffin tis- 

 sue in the human heart; and Timlin (Anat. Auz., 46, 22, 1914) reports 

 a paraganglion in the striped muscle of the upper portion of the esoph- 

 agus of man. In typical paraganglia the polygonal cells are arranged 

 in irregular cords which form a fine-meshed network, the areolas of 

 which are occupied by sinusoidal blood-vessels, upon which the cells rest 

 directly without the intervention of a basement membrane. The spher- 

 ical nucleus is poor in chromatin; the rcticular cytoplasm contains the 

 pheochrome granules. The internal secretion of the paraganglia de- 



FIG. 491. MEDIAN SECTION THROUGH THE 

 ANLAGES OF THE HYPOPHYSIS CEKEBRI 

 OF A 10 MM. CAT EMBRYO. (Bonnet.) 



Di, diencephalon; Te, telencephalon ; 

 3/~, mouth; R, Rathke's pouch (pituitary 

 anlage); I, infundibulum. X 50. 



