204 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
nephros and liver, in that between the sinusoids there is only one 
kind of cell. The fact that the cells in the trabeculae are all of one 
and the same kind, is well shown in Fig. 9. In another human 
Fig. 9. Human embryo of about two months. Part of a transverse section 
of the ventricle of the heart, t., £., muscular trabeculae ; Si ., sinusoid. Har¬ 
vard Embryological Collection, No. 38, section 185. 
embryo, of almost precisely the same age, I observe the same struc¬ 
ture of the trabeculae; this latter embryo was obtained very fresh, 
and the preservation histologically is extremely good, Zenker’s fluid 
having been used; it is No. 181 of the Harvard Embryological 
Collection. 
I have examined the ventricular trabeculae in the hearts of sev¬ 
eral young embryos of the rabbit, pig, and chick, and have found 
them in every case to consist only of young muscle cells with an 
endothelial covering. A negative assertion of this kind is of course 
liable to be incorrect, but it will, I believe, be found sufficiently 
exact to prove the importance of the heart sinusoids, by the absence 
