CHAPTER III. 



ON THE SITUATION AND STRUCTURE OF THE THYMUS GLAND. 



SECT. 21. THE term gland has been given to certain parts 

 of an animal body, that are by nature destined to separate 

 fluids of different properties from the general mass of blood, 

 which are to be applied to the various purposes of the animal 

 economy, or to be excreted, as being either useless or hurtful 

 to the constitution. 



SECT. 22. But though the term gland is properly given only 

 to such parts as are known to perform this office, yet it has 

 also been applied to some parts whose uses are unknown ; be- 

 cause their structure being apparently the same with that of 

 glands, (properly so called,) it has thence been conjectured that 

 their uses might likewise be similar. Thus the thymus has 

 acquired the name of gland. In like manner we use the terms 

 thyroid glands and glandulse renales (cxxm). For when- 

 ever any part receives more blood than is necessary for the 

 immediate growth or nourishment of that part, it is concluded 

 a priori that this blood is to undergo some change, or that 

 some secretion is to be made from it ; and for these reasons 

 the appellation of gland has been given to the thymus, the 

 thyroid, and glandulse renales. 



SECT. 23. The thymus is situated in the superior part of 

 the chest, in that space called the anterior mediastinum ; which 

 in the foetus-state, and for a few years after birth, is large. 

 The shape and size of this gland is various, differing in almost 

 every subject. It is triangular, adapted to the space between 



(cxxm.) As to the probable use of the supra-renal glands, and the 

 nature of their secretion, see ' London Medical Gazette/ June 21, 1844, 

 p. 411. A description, with figures, of the elementary molecules so 

 abundantly produced in these glands, is given in the Appendix to 

 the English edition of Gerber's 'Anatomy,' p. 103; and a notice of the 

 constitution of similar molecules in Note LX, p. 88. 



