PITUITARY BODY AND PINEAL GLAND. 485 



ruptured, when their contents exude in the form of an opalescent fluid, sometimes called 

 the thymic juice. 



Anatomists are somewhat divided in their opinions with regard to the structure 

 of the central cord and the lobules. Some adopt the view advanced by Sir Astley 

 Cooper, that the cord has a central canal connected with cavities in the lobules ; while 

 others believe that the cavities thus described are produced artificially, by the processes 

 employed in anatomical investigation. The latter opinion is the latest and is probably 

 correct. 



The blood-vessels of the thymus are numerous, but their caliber is small, and the gland 

 is not very vascular. They are derived chiefly from the internal mammary artery, a few 

 coming from the inferior thyroid, the superior diaphragmatic, or the pericardial. They 

 pass between the lobules, surround and penetrate the vesicles, and form a capillary plexus 

 in their interior. The vesicles, in this respect, bear a certain resemblance to the closed 

 follicles of the intestine. The veins are also numerous, but they do not follow the course 

 of the arteries. The principal vein emerges at about the centre of the gland posteriorly, 

 and it empties into the left brachio-cephalic. Other small veins empty into the internal 

 mammary, the superior diaphragmatic, and the pericardial. A few nervous filaments 

 from the sympathetic system surround the principal thymic artery and penetrate the 

 gland. Their ultimate distribution is uncertain. The lymphatics are very numerous. 



Inasmuch as the thymus is peculiar to early life, one of the most interesting points in 

 its anatomical history relates to its mode of development. This, however, does not pre- 

 sent any great physiological importance and is fully treated of in works upon anatomy. 



Pituitary Body and Pineal Gland. 



These little bodies, situated at the base of the brain, are quite vascular, contain closed 

 vesicles and but few nervous elements, and are sometimes classed with the ductless glands. 

 Physiologists have no idea of their function. 



The pituitary body is of an ovoid form, a reddish-gray color, weighs from five to ten 

 grains, and is situated on the sella turcica of the sphenoid bone. It is said to be larger in 

 the foetus than in the adult, and in fo3tal life it has a cavity communicating with the third 

 ventricle. This little body has been studied by M. Grandry, in connection with the 

 suprarenal capsules. He regards it as essentially composed of closed vesicles, with fibres 

 of connective tissue and blood-vessels. The vesicles measure from ^jr to -^ of an inch 

 in diameter. They are formed of a transparent membrane, containing irregularly po- 

 lygonal, nucleated cells, and free nuclei. The cells are from -^J^ to yyV^ of an inch in 

 diameter. The nuclei are distinct, with a well-marked nucleolus, and measure about 

 -5-5*^ of an inoh. Capillary vessels surround these vesicles without penetrating them. 

 M. Grandry did not observe either nerve-cells or fibres between the vesicles. In old 

 subjects he found the peculiar concretions (sympexions) already described as existing in 

 the thyroid gland. 



The pineal gland is situated just behind the posterior commissure of the brain, between 

 the nates, and is enclosed in the velum interpositum. It is of a conical shape, one-third 

 of an inch in length, and of nearly the color of the pituitary body. It is connected with 

 the base of the brain by several delicate commissural peduncles. It presents a small 

 cavity at its base, and frequently it contains in its substance little calcareous masses, com- 

 posed of phosphate and carbonate of lime, phosphate of magnesia and ammonia, and a 

 small quantity of organic matter. It is covered with a fibrous envelope, which sends 

 processes into its interior. As the result of the researches of M. Grandry, it has been 

 found to present a cortical substance, entirely analogous in its structure to the pituitary 

 body, and a central portion, composed of the ordinary nervous elements found in the gray 

 matter of the brain. Its structure is regarded by Grandry as very like that of the medul- 

 lary portion of the suprarenal capsules. 



