260 FRANKLIN P. MALL 



complete, that is, it forms a syncytium. Although Mollier 

 believes that the capillaries of the liver arise from the mesenchyme 

 of the capsule, which is impossible, it answers our purpose to 

 state that he shows that the connective tissue of the liver develops 

 from the endothelial cells and not from other mesenchyme cells. 

 Those of us who see the primary vascular tree of the liver arising 

 from the endothelial wall of the omphalomesenteric veins by a 

 process of reduction of this large vessel to form sinusoids, recog- 

 nize Mollier's " origin" of capillaries of the liver as only a second- 

 ary contact between the sprouting capillaries when they reach 

 the mesenchyme of the capsule of the anlage of the liver. For 

 the present purpose it is clear that Mollier demonstrates also that 

 the connective tissue of the liver arises from endothelial cells. 

 This relationship has been amply confirmed by F. T. Lewis in 

 the liver of a human embryo 7.5 mm. long. 11 So for the liver the 

 chain is complete; throughout development the connective tissue 

 of the lobule is in direct continuity with the endothelial cells of 

 the blood capillaries and therefore they give rise to them. Within 

 the lobule there are only endothelial cells and epithelial cells and 

 no one finds the reticulum arising from the latter. 12 



In embryo No. 239 the endothelial fibrils are quite unequally 

 distributed throughout the heart. In the atria, as mentioned 

 above, they form but a very thin layer. In the atrial canal the 



11 Lewis, F. T., Entwicklung der Leber. Keibel-Mall, Handbuch der Entwickl., 

 Bd.2,1911. S. 397, fig. 291. 



12 Quite recently Mollier finds the endothelial cells and reticulum of the spleen 

 as one continuous reticulum from which he concludes that the endothelial cells 

 arise directly from the mesenchyme (Arch. f. mik. Anat., Bd. 76, 1911). The oppo- 

 site conclusion may be drawn equally well. I have published figures which corre- 

 spond with .Mollier's, giving at the same time a conclusive experiment to prove that 

 the circulation of the spleen is entirely through the pulp spaces; these have the 

 value of blood capillaries (Mall, Amer, Jour. Anat., vol. 2, p. 315). Pathologists 

 have been of the opinion that in endarteritis the intima thickens by a proliferation 

 of endothelial cells, and that connective tissue may arise from these cells. Mar- 

 chand has questioned the truth of this statement, but recently the subject has been 

 reinvestigated by Baumgarten (Arbeiten auf dem Gebeite der Pathologischen 

 Anatomic, Leipzig, 1904, Bd. 4) who showed t hat proliferation of endothelial cells 

 may form a thickening of the intima without any rupture of the elastica interna, 

 thus excluding entirely any participation of connective tissue cells in the process. 

 See also von Szily, Anatom. Hefte 35, 1908, Taf. 45-47. 



