THE DUCTLESS GLANDS 191 



origin, being formed in fetal life from the entodermal cells of the dor- 

 sal end of the throat fissure. 



Location. — The thymus gland lies anterior to the thyroid, the 

 latter Ijdng the deeper. 



Shape. — The thyroid consists of two lobes, which are imited by 

 connective tissue, and appears as a loop-like acinous gland lying 

 along the neck and near the region of the bronchi and the jugular 

 veins with fibrous extensions toward the head. 



Structure. — The gland lobes are divided into lobules, which con- 

 sist of a cortical and a medullary portion. The cortex consists 

 of nodules of compact lymphatic tissue similar to those found in the 

 lymph glands. These occupy the chambers formed by the septa 

 of connective tissue. In the medulla there are a number of spherical, 

 or oval bodies composed of concentrically arranged epithelial cells. 

 These are known as Hassall's corpuscles, and represent only the 

 remains of the original glandular epithelium. They are charac- 

 teristic of the thymus-gland. The thymus appears to be a type of 

 lymph organ. Lymph vessels are rare; a few blood-vessels on the 

 upper side form capillary nets. 



The Adrenal Gland (Fig. 54, F). Location. — The adrenal gland, 

 often called the supra-renal capsule, lies just anterior to the front 

 part of the anterior lobe of the kidney, adjacent to the testicles in 

 the male and to the ovary in the female. It is loosely attached by 

 connective tissue to the posterior aorta and to the vena cava. 



Shape. — It is yeUowish-brown or reddish-pink in color, small, 

 and of irregular formation. 



Structure. — The adrenal gland consists of a cortical and a med- 

 ullary portion, although these two parts are not distinctly marked. 

 The cortical portion has columns which extend deeply into the gland, 

 and the medullary portion sends columns into the cortical portion. 

 Therefore, the two substances, lying side by side, form a cord-like 

 structure. 



It is probable that the cortical portion is derived from the in- 

 growths of the peritoneum, and the medullary cords from the sym- 

 pathetic ganghon. 



The cells are cylindrical or polygonal in shape, with an eccentric 

 substance between the columns. The cords, or columns, form be- 

 tween them, elongated channels which extend into the interior of 

 the gland and end as blind or caecal extremities. Large ganglionic 

 nerve cells belonging to the sympathetic system occur near the sur- 



