1278 . SPLANCHNOLOGY 



in 30 mm. embryos. After birth the chromaphil organs degenerate but the para- 

 ganglia can be recognized with the microscope in sites originally occupied by them. 



The paraganglia are small groups of chromaphil cells connected with the ganglia 

 of the sympathetic trunk and the ganglia of the celiac, renal, suprarenal, aortic and 

 hypogastric plexuses. They are sometimes found in connection wuth the ganglia of 

 other sympathetic plexuses. None have been found with the sympathetic ganglia 

 associated with the branches of the trigeminal nerve. 



The aortic glands or bodies are the largest of these groups of chromaphil cells 

 and measure in the newborn about 1 cm. in length. They lie one on either side of 

 the aorta in the region of the inferior mesenteric artery. They decrease in size with 

 age and after puberty are only visible with the microscope. About forty they dis- 

 appear entirely. Other groups of chromaphil cells have been found associated with 

 the sympathetic plexuses of the abdomen independently of the ganglia. 



The medullary portions of the suprarenal glands and the glomus caroticum 

 belong to the chromaphil system. 



The Suprarenal Glands (Glandulae Suprarenalis ; Adrenal Capsule) 



(Figs. 1183, 1184). 



The suprarenal glands are two small flattened bodies of a yellowish color, situated 

 at the back part of the abdomen, behind the peritoneum, and immediately above 

 and in front of the upper end of each kidney ; hence their name. The right one is 

 somewhat triangular in shape, bearing a resemblance to a cocked hat; the left is 

 more semilunar, usually larger, and placed at a higher level than the right. They 

 vary in size in different individuals, being sometimes so small as to be scarcely 

 detected : their usual size is from 3 to 5 cm. in length, rather less in width, and from 

 4 to 6 mm. in thickness. Their average weight is from 1.5 to 2.5 gm. each. 



Development. Each suprarenal gland consists of a cortical portion derived 

 from the celomic epithelium and a medullary portion originally composed of 

 sympatho-chromaffin tissue. The cortical portion is first recognizable about the 

 beginning of the fourth week as a series of buds from the celomic cells at the root 

 of the mesentery. Later it becomes completely separated from the celomic 

 epithelium and forms a suprarenal ridge projecting into the celom between the 

 mesonephros and the root of the mesentery. Into this cortical portion cells from 

 the neighboring masses of sympatho-chromaffin tissue migrate along the line of 

 its central vein to reach and form the medullary portion of the gland. 



'Relations. The relations of the suprarenal glands differ on the two sides of 

 the body. 



The right suprarenal is situated behind the inferior vena cava and right lobe of the 

 liver, and in front of the diaphragm and upper end of the right kidney. It is roughly 

 triangular in shape; its base, directed downward, is in contact with the medial and 

 anterior aspects of the upper end of the right kidney. It presents two surfaces for 

 examination, an anterior and a posterior. The anterior surface looks forward and 

 lateralward, and has two areas: a medial, narrow, and non-peritoneal, which lies 

 behind the inferior vena cava; and a lateral, somewhat triangular, in contact with 

 the liver. The upper part of the latter surface is devoid of peritoneum, and is in 

 relation with the bare area of the liver near its lower and medial angle, while its 

 inferior portion is covered by peritoneum, reflected onto it from the inferior layer 

 of the coronary ligament; occasionally the duodenum overlaps the inferior portion. 

 A little below the apex, and near the anterior border of the gland, is a short furrow 

 termed the hilum, from which the suprarenal vein emerges to join the inferior vena 

 cava. The posterior surface is divided into upper and lower parts by a curved ridge : 

 the upper, slightly convex, rests upon the diaphragm; the lower, concave, is in 





