THE SUPRARENAL BODIES. 



1801 



Fig 1522. 



Thymus 

 tissue 



thymus structure is largely replaced by fibrous and adipose tissue, vestiges of the 

 characteristic tissue, however, persisting (Fig. 1522). 



In addition to the chief anlage from the third pharyngeal pouch, a rudimentary 

 outgrowth occurs from 

 the ventral wall of the 

 fourth one. This anlage 

 may persist in man as 

 theparathynius , a small 

 body which occurs in. 

 close association, or 

 even encloses, the para- 

 thyroid derived from 

 the dorsal wall of the 

 fourth pouch. It 

 should be noted that 

 the close association of 

 the thymus and upper 

 parathyroids results in 

 a downward displace- 

 ment and transposi- 

 tion, so that, eventu- 

 ally, the upper parathy- 

 roids come to lie below 

 the original lower out- 

 growths. 



According to Beard, 

 Prenaut, Bell and 

 others, the transfor- 

 mation of the thvmus into a Ivmphoid organ occurs as the direct conversion of its 

 original epithelial elements into lymphocytes and not by invasion of pre-existing 

 lymphoid cells. While accepting such origin for the reticulum, Hammar^ and Max- 

 imow2 regard the lymphocytes as entering from without. 



Fat 



Thymus tissue 



Section of thymus body of man of twenty-eight, showing invasion and replace- 

 ment of thymus tissue by fat. X 20. 



THE SUPRARENAL BODIES. 



These are a pair of cocked-hat-shaped bodies situated at the back of the abdo- 

 men, on the inner aspect of the upper ends of the kidneys. Each has a base, or 

 ren.il surface, corresponding to the bottom of the hat, and an anterior and 2i posterior 

 surface, the basal borders of which are concave and look outward and downward. 

 There are an upper and a lower angle at either end of the base. The inner convex 

 border tends, especially in the right capsule, to present a third angle rather above 

 the middle. Thus the right one is more triangular and the left more crescentic. 

 They may be 6 or 7 cm. long and about half as broad. The thickness does not 

 probably often exceed 2 cm. The base is concave, adapted to the kidney, of which 

 if overhangs the anterior surface. The lower end is much thicker than the upper. 

 The concavity deepens above into almost a furrow filled by areolar tissue. The aji- 

 terior surface bears a deep fissure, the hilum, in the main parallel with the base, sub- 

 dividing it into two approximately equal regions. The posterior siaface is con- 

 siderably smaller than the anterior, owing to the projection of the latter over the 

 f'-ont of the kidney. It also presents a fissure nearly parallel with the base-line, but 

 neither extending the whole length of the organ nor so deep as the front one. 



In color the suprarenals are of a dirty yellowish brown and more or less pig- 

 mented. They weigh 6 or 7 gm. The left one is usually the larger. 



Relations. — The basal surfaces are on the kidneys. The posterior stirfaces 

 are against the diaphragm. The anterior surface of the right capsule has its lower 

 inner part behind the inferior vena cava. The part of the lower end near this may be 

 behind the duodenum. The remainder is in contact with the liver. The highest 



^Anatom. Anzeiger, Bd. xxvii., 1905. 



''Archiv. f. mik. Anat. 11. Entwick,,*Bd. 74, 1909. 



