1326 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS 



On the right it is irregular, straight or convex, and extends, dorsal to the liver, obliquely 

 cephalo-medially to meet the medial border in a more or less acute point, apex suprarenalis, 

 which is directed cephalically and somewhat medially. On the left the superior border is 

 irregularly convex in shape and nearly horizontal in direction. It passes gradually over into 

 the medial border without the intervention of any distinct apex. It is dorsal to the stomach 

 and in some cases comes into contact with the spleen. 



Accessory suprarenal glands [gl. suprarenales accessorise] are often found in the connective 

 tissue in the neighbourhood of the principal organs. They are also sometimes found in the 

 kidney near the internal spermatic veins and in the region of the sexual glands. The structures 

 recorded as accessory suprarenal glands may be complete suprarenal glands composed of the 

 cortex and medulla or they may be composed of the cortex only. Masses of chromaffin tissue 

 representing the medulla are sometimes spoken of as accessory suprarenale but these more 

 properly belong with the chromaffin system. 



Complete absence of the suprarenal glands has been recorded only in monsters with grave 

 cranial and cephalic defects. Absence of one gland has been found and the fusion of the two 

 has also been noted. 



Structure. — The suprarenal glands are surrounded by a thin and tough fibrous 

 capsule composed mainly of white fibrous connective tissue. From the capsule 

 numerous trabeculoe are given off which pervade the gland and form septa between 

 the groups and rows of cells. Within the capsule the suprarenal is composed of 

 an external firmer yellowish layer, the cortex [substantia corticalis], and an internal 

 softer whitish layer, the medulla [substantia medullaris] (fig. 1079). 



On section the cortex is seen to form by far the greater part of the gland and it is marked 

 radially from the centre toward the surface by darker and lighter streaks. In its deepest 

 part it is brownish yellow or red and is usually slightly torn where it joins the medulla. As 

 frequently found at autopsy the cortex is separated from the medulla by a sht filled with a 

 soft dark brown or blackish mass caused by the breaking down of the deeper layer of the cortex. 

 The medulla is a greyish, spongy, vascular mass which often because of its blood content appears 

 of a reddish or reddish-brown colour. 



The cortical portion of the gland is subdivided into a superficial, glomerular portion, 

 zona glomerulosa; an intermediate, fascicular portion, zona fasciculata; and an internal 

 reticula,r portion, zona reticulata, according to the peculiar grouping of the gland cells in these 

 respective areas. ' 



In the glomerular zone the cells are of irregular columnar shape, and grouped in coiled 

 columns. In the fascicular zone the cells, which are of polyhedral shape, are arranged in more 

 or less regular parallel columns, while in the reticular zone the cells form trabecute or groups. 

 The reticular connective-tissue framework, continuous with the capsule, surrounds the cell 

 masses and cell columns of the several zones. The cells of the medulla show an affinity for 

 chromic acid — chromaffin cells — and are grouped in irregular masses separated by septa of the 

 reticulum and venous spaces. The arteries form a close-meshed plexus in the capsule from 

 which branches run more or less parallel toward the medulla forming a network around the 

 cell columns of the glomerular and fascicular zones. This opens into a venous plexus of wide 

 calibre in the reticular zone, which is connected with the vessels of the medulla. Small medul- 

 lary arteries pass through the cortex without branching to end in a venous plexus in the medulla. 

 The abundant wide-meshed venous sinuses in the medulla (sinusoids) jom to form small 

 central veins which conA^erge toward the centre of the medulla to form the large central vein. 



Vessels and nerves. — The suprarenal glands are richly supplied with vessels. 

 The arteries are three — superior, middle and inferior. 



From the inferior phrenic artery, the superior suprarenal artery arises and passes toward the 

 superior border of the gland. From the aorta the middle suprarenal artery takes origin between 

 the coeliac and superior mesenteric arteries and passes toward the medial border of the supra- 

 renal. It is a branch of this artery which is usually found at the hilus along with the central 

 vein. From the renal artery the inferior suprarenal artery arises and reaches the suprarenal 

 near its base. These three arteries anastomose with one another and form a plexus in the 

 capsule of the suprarenal from which the arteries for the interior of the gland are derived. 



The large central vein from the medulla passes through the cortex to emerge at the hilus 

 as the suprarenal vein, vena suprarenalis. The right vein opens usually into the inferior vena 

 cava, where there is a valve, the left into the left renal vein. There may also be small branches 

 connecting with the phrenic or the right renal vein. 



The lymphatics of the suprarenals are very numerous and are represented by a superficial 

 plexus in the capsule and a deep plexus in the medulla. These are connected by numerous 

 anastornoses. They pass mediallj^ and converge into a number of trunks on each side which 

 empty into lymph-glands situated along the aorta near the origin of the renal arteries. On the 

 left side there is also the communicalion through the (li;ii)lir;)gni with a posterior mediastinal 

 gland. 



The nerves are derived chiefly from the cctliac and renal plexuses but include filaments 

 from the splanchnics, and according to some authors from the jihrenic and vagus nerves also. 

 These numerous fine twigs connect with the gland in many different places and form a rich 

 plexus. Branches are distributed to the capsule, to the cortical substance, and to the medullary 

 sub.stance. Groujjs of sympathetic ganglion cells arc found in tlie medullary part of the gland. 



Development. — The suprarenal glands of mammals have their origin from two sources. 

 The cortical mesodormic portion of the gjjinds arises in early embryos as buds extending from 



