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THE POPULAR SCIENCE MONTHLY. 



supplies both sides of the head (see Fig. 7, A), the artery supplying 

 the left arm coming off as usual. This is the normal condition in apes, 

 hears, dogs, and all the feline tribe. In some rare cases in man one 

 branch only comes off from the aortic arch, and this, again, divides 

 into the various arteries supplying the head and arms. In horses and 

 other solipeds, we see this form of aortic arch (see Fig. 7, D). Again, 

 the branches may all be given off separately from the arch, as is the 

 arrangement in the walrus (see Fig. 7, G). 



I have three times met with rather a rare anomaly of the great 

 veins going to the heart from the upper part of the body. The usual 

 A B 



R-C.Ai -^-^ 



R.S 



L.S 



D 



Fig. 7.— K. C, L. C, carotid arteries going to the head ; E. S., L. S., subclavian arteries going to 



the arms ; I, iunominate artery. 



arrangement in man, on each side, is for the great vein of one arm and 

 the corresponding side of the head to unite and form a single trunk 

 (brachio-cephalic), so we have two large venous trunks, one on each 

 side ; these two trunks then join to form a single large vessel, called the 

 superior vena cava, which empties its blood into the right side of the 

 heart (see Fig. 8, A). It occasionally happens that the great venous 

 trunks formed by the veins of the arm and head of each side do not unite 

 to form the superior vena cava, but each continues its downward course 

 and opens separately into the heart (see Fig. 8, B). On studying the 

 development of the blood-vessels, we find that in early fetal life this 

 condition of affairs exists, but after a time a transverse branch forms 

 between the two trunks. This branch gradually enlarges, while the 

 left trunk shrivels up, and at birth is only represented by a fibrous 

 cord. This anomaly of the veins we find, then, is a persistence of a 

 usually transient fetal condition in man, and also that in all birds and 

 many of the lower mammals it is the permanent condition. 



