1346 THE DUCTLESS GLANDS. 



crossed by the pancreas and splenic vessels. Sometimes these structures lie at a 

 lower level, when the whole antero-lateral surface is covered by peritoneum of the 

 omental bursa. 



Blood and Lymph Vessels. Typically, each gland receives three arteries : one direct from 

 the aorta, one from the inferior phrenic, and one from the renal artery ; and is drained by one 

 vein, which emerges at the hilum, the right to join the vena cava inferior, the left to join the 

 left renal vein. Numerous lymph vessels pass from the suprarenal glands to the lateral aortic 

 lymph glands. 



Nerves. The nerves passing to and from the glands constitute the suprarenal plexuses. 

 They connect with the. renal and cceliac plexuses and with the cceliac ganglia, and include 

 numerous fibresTrom the greater splanchnic nerves, with a smaller number from the vagus and 

 phrenic nerves. Most of them are medullated, but lose their sheaths on passing into small 

 ganglia in, or just within, the fibrous capsule of the gland. Thereafter they pass to the 

 chromaphil tissue of the medulla, either directly, or after first supplying the cortex. 



Structure. A suprarenal gland consists of a highly vascular central mass of chromaphil 

 tissue, the medulla, enclosed within a thick capsule of cortical substance, the cortex, which in 

 turn is enclosed within a capsule of fibrous tissue, tunica fibrosa. From the deep aspect of the 

 fibrous tunic trabeculaa pass inwards to support the glandular tissue. In the superficial part of 

 .the cortex the trabeculae interlace freely to enclose rounded loculi, zona glomerulosa ; in the 

 intermediate part they run vertically to the surface to enclose columnar spaces, zona fasciculata ; 

 in the deepest part of the cortex they become broken up and form a reticulum, zona reticulata. 



The cortex consists of polyhedral cells arranged in the interstices of the fibrous trabeculae. ; 

 These cells contain a lipoid substance, which is present in sufficient quantity to give the cortex a 

 yellow colour. 



The medulla is formed of a spongework of cell columns bounding anastomosing venous j 

 sinuses. The cells are large, contain numerous granules, and possess the specific chromaphil \ 

 reaction. In a fresh gland the medulla is of a dark red colour owing to the presence of blood in ; 

 its sinuses. 



- The blood-vessels enter at numerous points in the fibrous capsule and run in the trabeculae, | 

 forming a network around the cell masses and columns of the zona glomerulosa and zona ,j 

 fasciculata. ^n the zona reticulata the blood-vessels open up to form a venous plexus, which is 

 continued through large sinuses in the medulla to reach a central vein. This is the vein 

 which emerges at the hilus. 



Development of the Cortical System and of the Suprarenal Glands. The cortical system 



is a Derivative of the ccelomic epithelium (mesoderm). The first indication of its development 



is given, when the embryo is about 6 mm. in length, by the rapid proliferation of the epithelial 



cells placed between the mesonephros and the root of the mesentery. Numerous buds form and 



-penetrate the mesenchyme at the sides of and ventral to the aorta. In an 8-rnm. embryo these 



buds have already lost their connexion with the coelomic epithelium. By the time the embryo 



is 9 mm. long the developing cortical masses are vascularised. In man the greater part of the 



tissue thus formed is ultimately included in the cortex of the suprarenal glands, but small 



_ may escape, either at this stage or subsequently, to form independent cortical bodies. 



In 12 -mm. embryos the developing suprarenal glands lie in a caudal ward continuation of the 

 dorsal portion of the pleuro-peritoneal membrane called the suprarenal ridge, and are composed of 

 cortical tissue only. When the embryo is about 20 mm. in length sympatho-chromaphil cells, 

 destined to form the medulla of the gland, begin to migrate into the developing cortex. The 

 two kinds of tissue are in contact in 10-12 mm. embryos, but penetration of cortical masses by 



- sympatho-chromaphil cells has not been observed earlier than the stage mentioned. 



At first the immigrating cells are scattered in numerous columns and strands, and it is not 

 until the embryo is about 10 cm. in length that they begin to reach the central vein and to form a 

 true medulla. When the process of immigration ceases is unknown, probably not until after birth. 



The final specialisation of the cortex is a late phenomenon, and does not take place until long 

 after birth. The zona reticularis develops early and is recognisable in a 15-mm. embryo ; the 



- zona glomerulosa is not formed until the second or third year, but is represented until then by a 

 layer of small incompletely specialised cells immediately under the fibrous capsule. 



During foetal life the cortex is relatively enormous. This is due to a great proliferation 

 the cells of the fcetal zona reticularis, which differ from the adult cells of the same zone in 

 containing lipoids. This foetal cortex begins to undergo a fatty degeneration soon after bii 

 . and by the end of the first year has disappeared. The new cortex which replaces it develc 

 from the small, superficially placed, incompletely specialised cells already referred to. 



Comparative Anatomy of the Chromaphil and Cortical Systems. A knowledge of the 

 main facts of the comparative anatomy of the chromaphil system is a help to understanding its 

 distribution in man. Chromaphil tissue is first recognised with certainty in the cyclostomata, in 

 which it is arranged in thin strips on the walls of the larger .arteries and their branches. In 

 elasmobranchs chromaphil bodies are present and are arranged segmentally on branches of 

 'the aorta in close relation to the ganglia of the sympathetic chain. Cortical tissue is also re- 

 cognisable in the cyclostomata, in which it is arranged in small lobulated masses in the walls o ; 

 the posterior cardinal veins and renal arteries. Even in this rudimentary form it is rich ii 

 lipoids. In the rays (elasmobranchs) the cortical system is represented by a pair of yellow- 

 coloured, rod-shaped structures in the region of the kidney. In batrachians the chromaphil am' 

 cortical representatives first begin to come together. In the frog the adrenals are golden yellow 



