256 FRANKLIN P. MALL 



Tandler speak of these fibrils but they give no very definite infor- 

 mation regarding their nature. In his study of the chick His 5 

 describes the space between the endothelial tube and muscular 

 wall of the heart, which later in development fills with connective 

 tissue arising from the inner tube. In the atria, where this space 

 is never pronounced, the secondary thickening is also insignifi- 

 cant. Later His 6 also observes this space in young human em- 

 bryos. Many fibrils extend from the endothelial tube, which 

 when they are pronounced, draw out the side of the tube in a char- 

 acteristic way. This he pictures. He is uncertain whether these 

 fibrils are natural or produced by the hardening reagents used. 

 In the atrium the inner tube hugs the muscle wall closely. In the 

 atrial canal the space is filled with two pronounced cushions of 

 connective tissue, while in the ventricle the muscle forms trabec- 

 ule which are soon covered with endothelium. In the bulb 

 this space is very marked and filled with a delicate connective 

 tissue framework. He does not show conclusively the meaning 

 of this tissue. 



Tandler 7 describes and figures this substance well in a human 

 embryo with fifteen somites. Although his figure shows beauti- 

 fully the inwandering of nuclei from the endothelium, and al- 

 though he speaks of a reduction and enlargement of these filbrils, 

 he is unwilling to decide whether or not they are due to the method 

 of preservation and of staining of the sections. He states ex- 

 pressly that the tissue resembles very much Wharton's jelly. It 

 seems to me, however, that the evidence of His and Tandler is 

 sufficient to show that this tissue is not due to coagulation but 

 a constant normal constituent of the developing heart. That it 

 is distributed in a definite way in different portions of the heart 

 and in different stages of development speaks almost conclusively 

 for this opinion. Its origin and meaning is however a different 

 question. 



5 His, Untersuch ueber die erste Anlage des Wirbelthierleibes. Leipzig, 1868, 

 S. 141. 



,; His, Anat. mensch. Embryonen. Th. 3, 1885, S. 141. 



7 Tandler, Entwicklungsgeschichte des Herzens. Keibel-Mall Handbuch d. 

 Entwicklg. d. Menschen, Leipzig, 1911, Bd. 2, 8.524. 



