MINOT : SINUSOIDAL CIRCULATION. 
205 
of ordinary capillaries. Under these circumstances we must assume 
that the nourishment of the heart is direct from its own contained 
blood, and that it is only later that capillaries appear. The cardiac 
sinusoidal circulation is important, and this appears in physiolog¬ 
ical experiments on the frog’s heart, and, as Prof. W. T. Porter 
informs me, also in the mammalian heart after the exclusion of the 
coronary circulation. 
What then are the conditions in the adult? Are the sinusoidal 
blood spaces preserved ? Are the adult trabeculae covered merely 
by endothelium ? I have sought in the text-books and in special 
articles in vain for definite answers to these questions. The 
answers must be furnished by future research. I have, however, 
examined the heart ventricle in two frogs, Rana hcdecina , one cut 
in transverse, the other in longitudinal, section. The main central 
cavity in these sections is quite small; the greater part of the ven¬ 
tricle is occupied by a sponge-work of muscular trabeculae covered 
by endothelium, which bounds the blood channels, as described by 
Gaupp (.Anatomie des Frosches , Abtli. II, p. 256). I can also 
confirm Engelmann, who says (Arch. N4erl. Sci. Exactes, XI, p. 61) 
“ partout, jusqu’a une tr&s petite distance (environ 0.02 mm.) de 
l’ectocarde, la substance musculaire du ventricule et travers4e de 
fentes capillaires, qui cominuniquent avec la cavitfi ventriculaire et 
qui sont tapissees d’un prolongement de l’endothelium de cette der- 
ni&re.” Examination of the sections shows that the endothelium is 
everywhere fitted close against the muscle cells, apparently with no 
connective tissue under it, and shows also that the trabeculae con¬ 
sist practically only of muscle cells. There are, to be sure, a few 
scattered pigment cells, and a few nuclei, which may possibly 
belong to mesenchymal cells, though I think not; but it is certain 
that the trabeculae consist essentially of fibrillated muscle cells. 
In short, the adult frog’s heart has a typical sinusoidal circulation, 
which morphologically is identical in kind with that of the embry¬ 
onic human heart, Fig. 9. The organization comprises endothelial 
blood spaces with the spaces between them occupied with one kind 
only of parenchymal cells (i. e. muscles). 
5. Supra-renal capsules. The circulation of this organ is dis¬ 
tinctively sinusoidal, that is to say, the vessels are wider than true 
capillaries, and the endothelium is closely fitted against the paren¬ 
chyma formed by the supra-renal cells. By way of illustration I 
insert Figs. 10 and 11. Fig. 10 is from the cortex of the supra-renal 
