PHYSICAL ain LITERARY. 431 
quor ‘into the veins} or they may be filled 
from the arteries, tho’ with much greater 
difficulty, as happened in our injection ::when 
ftretched, they appear of a fpheroidal fhape ; 
and, the diameter of their orifices being lefs 
than that: of their cavities, we may give 
them the name of fimufes—Upon  diflecti- 
on,’ we obferve arteries opening, at leaft 
into fome of them, as I fhall afterwards 
prove, and confiderable veins are continued 
from all of them ; the veins and “fnufes ha- 
ving all large communications with each o- 
ther ; and, tho’ fome of the finufes may have 
only two or three fmall veins opening into’. 
them, yet, in general, the diameter of the 
veins continued from them, is not eas in- 
ferior to that of the finus. 
Since, from this ‘defcription, it appears, 
that thefe cavities are only the fomewhat di- 
lated extremities of the branches of the veins; 
we may account for their formation, from 
the more than ordinary difficulty there is in 
the return of the blood from the gravid ute- 
rus; which being. therefore accumulated, 
muft ftretch all the veins greatly,’ but fuch 
» parts of them moft as refift the leaft ; confe- 
quently their extremities, which are only co- 
vered 
