ORGANS OF THE BODY. 



423 



latter and the follicles of the mucous membrane is almost complete. The 

 latter may be regarded as small lymphatic glands occurring in mucous 

 membranes, with which view the simi- 

 larity of the pathological changes occur- 

 ring in them to those observed in lym- 

 phatic glands, is in perfect accordance. / 



228. 



The thymus gland, a double organ 

 whose function is unknown, and which 

 is, as far as we are at present aware, 

 similar to a lymph node in structure, 

 exists in full development only during 

 the earlier periods of life, falling, later 

 on, more and more a prey to fatty de- 

 generation. Thus it is only exceptionally 

 to be recognised in the bodies of older 

 individuals. 



The first point which we observe in 

 the structure of the organ is that, besides 

 being exquisitely lobulated, it possesses 

 a very vascular fibrous envelope. Owing 

 to the fact that the latter invests the 

 internal mass but very loosely, the glan- 

 dular tissue of each half of the organ 

 may, after severance of the blood-vessels, 

 be disentangled from it in the form of a 

 band-like skein. The latter consists 

 everywhere of a venous and arterial twig 

 of accompanying lymphatic vessels, and 

 a peculiar gland-duct, known as the central canal, upon which are situated, 

 externally, the lobes and lobuli of the gland. When dissected out, the 

 whole is of considerable 

 length (fig. 416, 1). The 

 central canal, which, accord- 

 ing to His, has in the calf 

 a diameter of only 0-7444 

 mm., is twisted up into a 

 kind of spiral in the natural 

 state, and the lobes are in 

 close contact with one an- 

 other. 



If we proceed with our 

 analysis, we find that each 

 lobe is made up of a num- 

 ber of smaller lobuli, and 

 the latter, enclosed within 

 a vascular envelope of con- 

 nective-tissue, are again 



composed of Smaller poly he- Fig. 417. Portion of the thymus of a calf (after His), showing 

 , , r a 4.4. A the arterial, a, and venous rings, &; the capillary network, 



dral Structures, flattened c; and the cavities of the acini, d 



one against the other, whose 



diameter is 0-5640-M128 mm., or, in the calf, 1-1128-2-2256 mm. 

 28 



Fl. 416. 1. Upper portion of the thyimis 

 of a foetal pig of 2" in length, showing 

 the bud-like lobuli ar.d glandular ele- 

 ments. 2. Cells of the tliymus, mostly 

 from man ; a, free nuclei ; b, small cells ; 

 c, larger; d, larger, with oil globules, 

 from the ox; ,/, cells completely filled 

 with fat at /, without a nucleus ; g, h, 

 concentric bodies ; g, an encapsuled nu- 

 cleated cell; A, a composite structure of 

 a similar nature. 



