THE THYMUS 133 



after birth. Aluch remains to be done to determine the exact 

 natnre of the elements (•omi)()sin<^ this ()r<i;an. 



In the mechilhi of man\- h)l)nles, fnsiform cells are concentrically 

 arranji:e(l to form smaller cell masses known as Ilassal's corpuscles. 

 In the center of some there may be deposits of calcium or small 

 cysts surrounded by flattened cells. The significance of these bodies 

 is debated. 



The thymus differs from other lymph organs in that it has no 

 nodules and no lymph sinuses. 



The thynuis normally begins to degenerate in the adult animal, 

 although there is considerable individual variation in the extent to 

 which such involution has proceeded at particular ages. The 

 lymphoid tissue becomes progressively less prominent, and con- 

 nective tissue containing fat cells occupies much of the structure. 



Despite many endeavors to discover the exact function of the 

 thymus, there are as yet no clear-cut results. Many students are 

 inclined to regard it as an endocrine gland, but at present there is 

 no good e^'idence in proof of this conclusion. 



REFERENCES. 



Basir, M. a. 1932. The histology of the spleen and siiprarenals of Echidna, 



Jour. Anat., 66, 628. 

 Danchakoff, Vera. 1916. Equivalence of different hematopoietic anlages. 



Am. Jour. Anat., 20, 255. 

 Downey, H. 1922. The structure and origin of the lymph sinuses of mam- 

 malian lymph nodes and their relations to endothelium and reticulum, 



Haematologica, 3, 31. 

 Drinker, C. K., and Field, M. E. 1933. Lymphatics, Lymph and Tissue 



Fluid, Baltimore, The Williams & Wilkins Company. 

 Job, T. T. 1922. Studies on lymph nodes, Am. Jour. Anat., 31, 125. 

 Jordan, H. E. 1934. Hemal nodes in man, Anat. Rec, 59, 297. 

 Kingsbury, B. F. 1932. The developmental significance of the mammalian 



pharyngeal tonsil: cat, Am. Jour. Anat., 50, 201. 

 Krumbhaar, E. B. 1926. Functions of the spleen, Physiol. Rev., 6, 160. 

 Myers, M. A. 1928. A study of the tonsillar developments in the lingual 



region of anurans, Jour. Morph. Physiol., 45, 399. 

 Rothermel, J. E. 1930. A note on the megakaryocytes of the normal cat's 



spleen, Anat. Rec, 47, 251. 

 Snook, T. 1934. The development of the pharyngeal (human) tonsil. Am. 



Jour. Anat., 55, 323. 

 Tehver, J., AND Graham, T. The capsule and trabecuhe of the spleen of 



domestic animals. Jour. Anat., 65, 473. 

 Van der Jagt, E. R. 1932. The origin and development of the anterior 



lymph sacs in the sea turtle, Thalassochelys caretta. Quart. Jour. Micr. 



Sci., 75, 151. 



See Appendix for general text references. 



