460 OF ABSORPTION AND SANGUIFICATION. 



the two organs respectively. For the Supra- Renal bodies attain a very large 

 size in foetal life, surpassing the Kidneys in dimension up to the tenth or twelfth 

 week of Human embryonic development ; though they afterwards diminish so 

 much, relatively to the Kidneys, as to possess in the adult condition only 1-2 8th 

 part of their bulk. 



486. The elementary structure of the Thymus Gland may be best understood 

 from the simple form it presents, when it is first capable of being distinguished 

 in the embryo. It then consists of a single tube, closed at both ends, and filled 

 with granular matter; and its subsequent development consists in the lateral 



A section of the Thymus gland at the eighth month, showing its anatomy ; from a preparation of Sir A. 

 Cooper's : 1, the cervical portions of the gland ; the independence of the two lateral glands is well marked ; 

 2, secretory follicles seen upon the surface of the section ; these are observed in all parts of the section ; 3, 3, 

 the pores or openings of the secretory follicles and pouches; they are seen covering the whole internal surface 

 of the great central cavity or reservoir. The continuity of the reservoir in the lower or thoracic portion of the 

 gland with the cervical portion is seen in the figure. 



growth of branching offshoots from this central tubular axis. In its mature 

 state, therefore, it consists of an assemblage of glandular follicles, which are 

 surrounded by a plexus of bloodvessels; and these follicles all communicate 

 with the central reservoir from which, however, there is no outlet. The cavities 

 of the follicles contain a fluid, in which a number of corpuscles are found, giving 

 it a granular appearance. These corpuscles, the diameter of which varies from 

 l-5750th to l-2550th of an inch, usually averaging between l-4000th and 

 l-5000th, are for the most part in the condition of nuclei; but fully-developed 

 cells are found among them, at the period when the function of this body seems 

 most active. The chemical nature of its contents, at this period, closely resem- 

 bles that of the ordinary protein compounds. The Vascular supply of this 

 organ, during the period of its functional activity, is extremely abundant ; and 

 the capillary network into which the arterial branches subdivide closely sur- 

 rounds the exterior of the follicles, arid is so exceedingly dense that its meshes 

 are of less diameter than the vessels themselves. The Lymphatics are large, 

 and communicate directly with the Vena Cava ; but their immediate connection 

 with the cavity of the Thymus body has not yet been demonstrated. It has 

 been commonly stated, that the Thymus attains its greatest development, in 

 relation to the rest of the body, during the latter part of foetal life ; and it has 

 been considered as an organ peculiarly connected with the embryonic condition. 

 But this is a mistake ; for the greatest activity in the growth of this organ 

 manifests itself, in the Human infant, soon after birth ; and it is then, too, that 

 its functional energy seems the greatest. This rapid state of growth, however, 



