STUDIES OF HEMAL NODES 



VII. THE DEVELOPMENT AND FUNCTION OF HEMAL NODES 



ARTHUR WILLIAM MEYER 



From the Division of Anatomij of the Stanford Medical School 



FIFTEEN FIGURES 



Some years since when hemal nodes were found in close prox- 

 imity to the parath^nnus glands in the sheep, it was thought 

 that these nodes would be particularly valuable for a study of 

 development. Unfortunately, however, these nodes also are 

 very inconstant in occurrence and here as elsewhere in the 

 sheep, they are often closely associated with lymph nodes. 

 Indeed, the greatest obstacle in the study of the development 

 of hemal nodes is not the protean structure of the nodes of 

 adult animals but the inconstancy in their occurrence and posi- 

 tion. This is true not only in the adult animal but in foetuses 

 as well, for although a large number of sheep foetuses of vary- 

 ing ages and also new born lambs were carefully dissected, not 

 a single hemal node was ever found to be constant in position. 

 The same statement holds for Bos taurus. Besides, the fre- 

 quent close association of lymph and hemal nodes makes dif- 

 ferentiation of the early stages in development naturally very 

 difficult. To partly obviate these difficulties it was decided 

 to trace back as far as possible in the foetal development of the 

 sheep, the occurrence of nodes which could with some certainty 

 be recognized macroscopically as such in the fat of the lumbar 

 sub-vertebral region. The tissues in this region were also ex- 

 cised en masse in younger foetuses for purposes of microscopi- 

 cal study in order to determine, if possible, by means of serial 

 sections the earlier stages in the development of hemal nodes 

 which because of their small size caimot be recognized with the 

 unaided eye. For the latter purpose small foetuses were also 



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THE AMERICAN JOURNAL OF ANATf)MY, VOl,. 21, NO. 3 



