Ill' ART. 



599 



origin.) It tlien proceeds into the concavity of 

 the arch of the aorta, and as it is abaul t.) pa-s 

 through tin: tihruiis coat of the pericardium, it 

 divides into its two branches, the right and 

 left. The left branch passes in front of the 

 descending portion of the arch of the aorta to 

 reach the left lung ; the right branch passes 

 brlnnd the ascending portion of the arch to 

 reach the right lung. In the fa-tus the pulmo- 

 nary artery divides into three branches, the 

 two we have just mentioned, and a third, the 

 ductus arteriosus, which unites the pulmonary 

 artery to the descending portion of the arch, 

 in oilier words, after the aorta has given oft" the 

 ranches to the head and superior extre- 

 mities. The descending cava, immediately 

 before it perforates the fibrous coat of the peri- 

 cardium, crosses the right branches close upon 

 the bifurcation of the trachea ; within the peri- 

 cardium it lies on the right side of the ascend- 

 ing portion of the arch of the aorta. The 

 inferior cava is seen perforating the cordiform 

 tendon of the diaphragm, and almost imme- 

 diately afterwards it enters the posterior and 

 inferior angle of the right auricle. The pul- 

 monary veins are placed inferior to the two 

 branches of the pulmonary artery. The two 

 right pulmonary veins pass behind the right 

 auricle to reach the left, which they enter near 

 the septum auriculorum. 



Pettttiaritiet of the fatal heart. (For an 

 account of the developement of the heart and 

 large bloodvessels see OVUM.) The heart of 

 the fo3tus before the fourth month is placed 

 vertically, but towards that period the apex 

 begins to turn towards the left side. The 

 auricular part of the heart is considerably larger 

 in proportion than the ventricular. The relative 

 size of the heart to the body at birth differs 

 considerably from that of the foetus at an earlier 

 period of its developement. According to 

 Meckel the relative size of the heart to the 

 body about the second or third month of uterine 

 life is 1 to 50; at birth and for a few years 

 aftfi wards as 1 to 120. The greater size of the 

 heart of the foetus seems to depend principally 

 upon the greater thickness of the walls of its 

 cavities. The great disparity between the thick- 

 ness of the two sides so very apparent shortly 

 after birth does not exist in the earlier periods 

 of uterine life, though also generally sufficiently 

 well-marked in the foetus at the full time. This 

 is explained by the circumstance that the two 

 sides of the heart at this period have nearly 

 equal obstacles to overcome in propelling the 

 blood.* In the earlier stages of its deve- 

 lopement the infundibuliform portion of the 

 right ventricle is less prominent than at a later 

 period. The left ventricle is at first a Iiltle 

 larger than the right ; at birth and for a short 

 while after they are equal. The two auricles 

 communicate with each other through the fora- 



In two foetuses, however, which I lately cxa- 

 mined, and where I had positive evidence that 

 they had not yel reached the sixth month of utcro- 

 gestation, the difference between the thickness of 

 the two ventricles of the heart was distinctly 

 marked. 



men ovule.* This foramen i at its maximum 

 *i/r :il><mt tin, 1 hixtli month. 



l'ii/i-f ii f tin /iiinmi'ii untie. Tills valve, 

 which, however, can scarcely be called a valve, 

 as it is a provision for effecting the obliteration 

 of the foramen ovale at the time the child 

 assumes its independent existence, first makes 

 its appearance at the lower part of the foramen 

 about the third month, or, according to Setiac 

 and Portal, about the second month. It is 

 formed by the inner membranes of the two 

 sides of the heart, containing some muscular 

 fibres between them, particularly at its lower 

 part. It is of a semilunar form ; its convex 

 edge adheres to a greater or less portion of the 

 margins of the valve as its growth is more or 

 less advanced ; its concave margin, which is 

 free and loose, looks upwards and forwards. 

 This valve may be said to belong almost exclu- 

 sively to the left auricle, as it is attached to 

 that margin of the foramen.f Though this 

 valve is of sufficient size at birth to shut the 

 foramen, yet its concave or upper margin is 

 easily depressed so as to leave a considerable 

 interval between it and the upper margin 

 of the foramen. We will find, from the man- 

 ner in which the valve is attached to the left 

 margin of the foramen, that it is much more 

 easily depressed by a current passing from the 

 right auricle into the left than in the opposite 

 direction. In fact any force of this kind ap- 

 plied in the opposite direction would rather 

 tend to keep the valve applied to the upper 

 edge of the opening; a circumstance which 

 occurs after birth when the blood flows along 

 the pulmonary veins into the left auricle, and 

 which must materially assist in producing com- 

 plete obliteration of the foramen. The manner 

 in which the blood passes between the auricles 

 through the foramen ovale in the foetus was the 

 subject of a violent controversy in France at 

 the termination of the seventeenth anil the 

 commencement of the eighteenth centuries. It 

 was first commenced between Meri on the one 

 side, who had proposed a new theory of the 

 foetal circulation by which the blood was made 

 to pass from the left auricle into the right, and 

 by Duverry and Fauvery on the opposite side, 

 who maintained the opinion of Harvey, and 

 which is now universally adopted, that it passes 

 from right to left. Many celebrated anatomists 

 and mathematicians attached themselves to the 

 opposite parties, and at last the controversy 

 extended itself to the neighbouring kingdoms. J 



Kustacliiun valve. This valve, the appear- 

 ance and position of which have been already 



This opening is frequently termed Iron tie Ratal 

 by the French writers though described by Galen. 



t This explains how the depression (fossa ovalis ), 

 marking in the adult the position of the valve, 

 should be better seen from the right than the left 

 auricle. 



} Those who may be anxious to acquaint them- 

 selves more fully with the nature of this contro- 

 versy and to examine the argument! adduced on 

 both sides may consult the Mt'-rnoires de 1'Arademie 

 for that period, and Sense's Traitc dc la Structure 

 du Cceur, torn. i. p. 369, and the Supplement in 

 torn. ii. 



