AND FAMILY DISPENSATORY. 99 
érr alfo fromthe truth: others fay, it is made of blood and chyle: but our opinion 
is, that it proceeds. from, and is generated of, the chylous juice, and aferous part of 
the arterial blood: for that thé ferofity of the arterial blood (and not the fubftance 
of the blood itfelf) does help to generate and conftitute the milk, we are induced to 
believe, not only from the foregoing reafon, but becaufe no anaftomofes of the arte- 
ries with the lacteal pipes of the dugs could ever yet be found out :.anditruly this 
opinion Bartholine feems to favour, where he faith, that all the blood which is pour 
ed out of the arteries into the breafts, is not turned into milk, but only themore fe- 
rous or wheyifh part thereof; the reft (that which ferves for nourifhment — 
running back again, by the veins into the heart. 
The membrane, called pleura, or inner covering of the ribs, is a meh die 
thin, hard, and refembling the peritonzum, but thicker and ftronger. Itarifesfrom 
the tunicles which cover the intercoftal nerves proceeding from the back-bone, by 
means of which it is continued with the coats of the brain: and therefore it. is 
thicker in the back, to whofe vertebra it cleaves as it were infeparably. It is every 
where double, that the veffels may be carried within the foldings thereof: the in- 
ner part, looking towards the lungs and inwards, is thickeft, fmoothett, and as it 
were bedewed with a waterifh humour, that it fhould not hurt the lungs by any 
roughnefs ; the outer part is thinner and rougher, that it might cleave the more 
firmly to the ribs : between thefe the matter of the pleurify is many times collected, 
and not only between the pleura and muicles. As to its figure, itis arched without, 
hollow within ; above it is narrower, below broader, principally towards the fides. 
From it arife fome nervous fibres, bywhich the lungs are tied to it; if thefe be too 
ftraight, the motion of the lungs is hindered, which caufes an incurable difficulty of 
breathing, Its ufes are tocover the whole cavity of the thorax, and render it {mooth, 
that the lungs might not be hurt; and to wrap in all the vital parts, and to defend 
them from all external injuries. The mediaftinum is a membrane ftanding in the mid- 
dle of the breatt, dividing the right fide from theleft. _ It arifes from the pleura, be- 
ing adouble membrane. Its fubftance is membranous, yet fofter than the pleura; 
its exterior part is rougher, becaufe of the fibres, by, which ats knits che Plearis 
but its inner fide, towards the lungs, is fmooth ; and about the veflels ic ‘ae 
ly full of fatlikethe caul. The ules of the mediaftinum are, waelecne te 
thorax into two parts, that, the: ‘breaft and lungs being hurt or epee bias 
the other might be fafe : fecondly, to hold up the pericardium firmly, ie; the z 
heart is contained, that it fhould not reft upon the back-bone, ep pik 
‘back y or, that it fhould fall’ uponthe breaft-bone, when we bend ourtelves iowa ® 
the ground ; ; nor touch the ribs, when we lie upon our fides eee id = mn id 
‘paffage to the'veffels which run through it; as alfo to futtain ee 
“fhould, by the weight of the bowels, be drawn too muc 
h donne 
