ORGANS OF THE BODY. 443 



From Remak's investigations as to its origin, it would appear that the 

 thyroid springs in the form of a saccule from the middle line of the anterior 

 wall of the pharynx, and is formed consequently in the same manner 

 primarily as the glands of the intestine. Soon after, however, it becomes 

 completely separated from the pharynx, and out of the single vesicle two 

 sacs are formed by division, which assume a lobulated appearance from 

 indentations and constrictions which are eventually developed on them. 

 In the thickened walls of these sacs solid aggregations of cells are subse- 

 quently formed, which are developed later on into the gland vesicles of 

 the organ, becoming invested with an envelope of connective-tissue, within 

 which a certain amount of fluid collects among the elements. The large 

 main vesicle on each side appears, likewise, to give origin to glandular 

 elements, by undergoing constriction at various points, and seems thus to 

 work its own obliteration. According to Peremescliko, we not unfre- 

 quently encounter division of the gland capsules as phenomena of growth. 

 The thyroid gland is probably at its greatest pitch of development in 

 the new-born infant, and becomes very sluggish in growth a few weeks 

 after birth. 



237. 



The suprarenal ladies (glandulce suprarenalcs) have, on the other hand, 

 a different origin from the last, namely, from the middle germinal plate. 

 These are double organs, in regard to whose functions we are totally in 

 the dark. Enclosed in a capsule they present considerable variety of sub- 

 stance, both from an anatomical and physiological point of view, and we 

 may distinguish a cortical and medullary portion. The cortical .sub- 

 stance is marked with radiating streaks in different animals, varying in 

 colour from a brown or reddish, down to a whitish yellow, and is of a 

 tolerably firm consistence. Contrasted with this the lighter greyish red 

 or whitish medullary portion is less resistent. In man a dark narrow 

 boundary zone may be observed between these two portions, usually 

 yellowish brown, but at times greenish or blackish brown. After death 

 this breaks down rapidly, and becoming fluid, causes the loosening of the 

 medullary part of the organ from the rest. 



The envelope (fig. 427, c) consists of connective- tissue with elastic 

 elements. Externally it merges into formless areolar tissue, containing 

 fat cells. Internally it gives off those numerous fibrous processes which 

 traverse the organ, and in their ultimate arrangement form a framework 

 within which the cells are enclosed. 



Let us now glance at the cortical substance of the suprarenal bodies. 



Those band-like processes just mentioned are tolerably strong, and take 

 a slightly convergent course inwards, giving to the cortex, which in man 

 is about 0'6767-(H279 in thickness, a fibrous appearance, distinctly 

 visible even to the unaided eye. From these numerous bundles of 

 connective-tissue coming off, laterally intercommunicate with others also 

 given off from the internal surface of the envelope, giving rise to a large 

 number of glandular cavities. Near the surface of the organ these latter 

 are generally short, but soon attain considerable length as they follow the 

 course of the septa, assuming a columnar figure (fig. 427, , b; 428, a). 

 In transverse section, however, these rows of cells do not always appear 

 round, but not unfrequently present to our view oblong, reniform, and 

 crescentic configurations. Again, in profile, we may easily make out that 

 such gland cylinders divide and give off branches at' acute angles. 



