CHAPTER XI. 



THE THYMUS GLAND. 

 BY E. KLEIN. 



IN Man and Mammals, at an early period of their existence, a 

 placentiform lobulated body, called the thymus gland, which in 

 point of structure must be associated with the peripheric 

 lymphatic glands, lies behind the upper part of the sternum, 

 and partly occupies the Incisura jugularis at the lower part of 

 the neck. It is invested by a capsule rather loosely con- 

 nected with the organ by means of vessels and fasciculi of con- 

 nective tissue, the thickness of which increases with the size 

 of the organ. The number and size of the lobes vary to a 

 considerable extent. In dogs, in the pig, and in the cat, there are 

 usually only two closely connected lobes of unequal size, which 

 present an acute edge externally and below, but are remark- 

 ably thick at their surfaces of contact. In the calf, on the other 

 hand, the organ consists of two oval placentiform- lobes not pre- 

 senting acute edges, and of nearly equal size, united together 

 by a short cylindrical intermediate portion. The thymus of the 

 new-born infant exhibits two or three lobes ; when there are 

 three, these are so arranged that a central thicker lobe has some- 

 times a larger and sometimes a smaller lobule on each side. 

 The several lobules of the thymus in man, as well as in the dog, 

 the cat, and the pig, may possess small appendices ; and the 

 fissures by which the lobes are produced are sometimes deep, 

 and sometimes less strongly marked. Each lobe is divided into 

 several lobules by fissures uniting at various angles, and these 

 again are subdivisible into the ultimate divisions termed acini, 

 alveoli, granules, or more correctly, follicles. 



The capsule exhibits the usual structure of membranous con- 

 nective tissue ; its elements are, wavy connective tissue fibres 



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