1154 THE DUCTLESS GLANDS. 
the anterior surface, as a rule conveys all the blood from the organ. On the right side it opens at 
once into the inferior vena cava, and on the left side into the left renal vein. 
The nerves of the suprarenal bodies are very numerous. They come from the solar plexus, 
and constitute the suprarenal plexus. 
Structure of the Suprarenal Capsule.—The suprarenal capsule is surrounded 
by a thin connective-tissue sheath, from the deep surface of which fine processes are given 
off which enter the substance of the organ, and form within it a supporting stroma or 
framework. 
The gland-substance is composed of—(1) an external cortical portion, firm in con- 
sistence, of a yellowish hue, and forming the chief bulk of the organ ;. and (2) an internal 
medullary part, very soft and pulpy, and dark brown in colour. 
The cortical substance (substantia corticalis) consists of groups of cells occupying the 
interstices of the stroma. These cell-groups present different forms at different levels 
from the surface. ‘Thus, subjacent to the connective-tissue sheath, there is a thin stratum, 
termed the zona glomerulosa, in which the cell masses are more or less rounded ; next 
comes the zona fasciculata, which constitutes the chief part of the cortex, and in which 
the cells are erouped i in long columns which are arranged radially with reference to the 
surface ; and lastly, there is the deepest layer, the zona reticularis, in which the cells are 
disposed in a reticular manner amidst the stroma, 
The medullary part (substantia medullaris) is also pervaded by a fibrous stroma 
continuous with that of the cortex. This forms an irregular meshwork, the spaces of 
which are occupied by cells of very variable shape and somewhat similar to epithelium in 
appearance. 
The arteries enter the cortex and break up into capillaries which are arranged around 
the cell-groups. In the medulla there are large thin-walled ee into which the 
whole blood of the organ passes. These capillaries are closely surrounded by the medullary 
cells. Proceeding from them are the radicles of the capsular vein. 
Development of the Suprarenal Capsule.—Several observers ascribe a totally 
different origin to the cortical and medullary parts of the suprarenal body. According 
to these authorities the medulla is derived as a column of cells which grows out from the 
sympathetic cord, and becomes in the process of development encapsulated within the 
cortex. That a portion of the sympathetic enters the suprarenal capsule would appear 
to be undoubted, but that it forms the medulla is questionable. Gottschaw and Janosik 
hold that the medullary cells are in reality derived by a metamorphosis of the cortical cells. 
The cortical part of the suprarenal body is formed from a mass of mesodermic cells 
which become grouped together in the immediate vicinity of the inferior vena cava soon 
after that vessel is formed. The cells thus accumulated together are said to be derived 
directly or indirectly from the epithelial cells which line the body cavity. Janosik and 
Mihalkovies believe that they come from the germ epithelium which covers the preaxial 
part of the genital ridge. According to Weldon, however, they owe their origin to columns 
of cells which grow out from the Malpighian ¢ clomeruli of the ‘preaxial part of the Wolffian 
body. 
THE: PEY RO TD BODE 
The thyroid body (glandula thyreoidea) is a highly vascular, pliant structure 
which clasps the upper part of the trachea and extends upwards for some distance 
upon each side of the larynx. In size it varies greatly in different individuals, and 
in the female and child it is always relatively larger than in the adult male. It 
consists of three well-marked subdivisions—yviz. two lateral lobes, jomed across the 
middle line by the isthmus. 
Each lateral lobe is conical in form. Its base extends downwards upon the side 
of the trachea as far as the fifth or sixth tracheal ring, whilst its apex rests upon 
the ala of the thyroid cartilage. Its superficial surface is somewhat flattened, and 
is clothed by the pretracheal layer of cervical fascia, from which the organ derives 
a sheath, and also by the sterno- thyroid, sterno-hy oid, and omohyoid muscles. It 
is also overl: apped by the sterno-mastoid muscle. Its deep surface is adapted to the 
parts upon which it les—viz. to the side of the trachea, to the cricoid cartilage, and 
to the inferior cornu and adjoining part of the surface of the ala of the thyroid 
cartilage; whilst its posterior border extends backwards so as to touch the ceso- 
phagus and pharynx and overlap the common carotid artery (Fig. 626, p. 924). 
Cc 
The isthmus of the thyroid body is a narrow band of varying width which lies 
