Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/281

 O M Y. 237 Part IV. A N A r Laftly, the peroniea continuing its courfe downward, From thence it runs outward, and a little above the on the backfide of the fibula, as far as the os calcis, outer ankle communicates with the tibialis anterior by forms an arch with the tibialis pofterior, between the a- an arch, which fends feveral fmall ramifications to the neighbouring parts. Hragalus and the tendo-achillis. PAR OF

THE

T

IV.

VEINS.

TH E blood, diftributed to all parts of the body by curvature of the aorta. At this place it terminates by two kinds of arteries, the aorta and arteria pul- a bifurcation or divifion into two large branches or fubmonaris, returns by three kinds of veins, called by ana- ordinate trunks, one of which runs toward the left hand, tomifts vena cava, vena portae, and vena pulmonaris. the other toward the right. The vena cava carries back to the right auricle of the Thefe two branches are named fubclavia, as lying beheart, the blood conveyed by the aorta to all parts of the hind the clavicuhe. body except what goes by the arterias coronarbe cordis. The trunk of the fuperior cava, from where it leaves It receives all this blood from the arterial ramifications in the pericardium to the birfurcation, fends out anteriorly part diredtly, and in part indiredtly. leveral fmail branches. Thefe branches are the vena The vena portae receives the blood carried to the mediaftina, pericardia, diaphragmatica fuperior, thymica, floating vifcera of the abdomen by the arteria cseliaca mammaria interna’, and trachealis. and the two mefentericae, and conveys it to the> vena All thefe fmall branches from the trunk of the cava hepatica, and from thence to the vena cava. fuperior are termed dextrae-, and their fellows on the oThe vena pulmonaris conveys to the pulmonary finus, ther fide, called finiftrae, do not arife from the trunk, or left auricle of the heart, the blood carried to the but from the left fubclavia. lungs by the arteria pulmonaris., Pofteriorly, a little above the pericardium, the trunk We commonly talk of the ^|na cava in general, as if of the fuperior cava fends out a capital branch, called it were but one vein at its origin, or had but one com- vena azygos, or vena jins pari, which runs down on the mon trunk; whereas it goes out from the right auricle right fide of the bodies of the vertebrae dorfi, almoft to of the heart by two large feparate trunks, in a direftion the diaphragm ; giving off the greateft part of the, venae almoft perpendicularly oppofite to each other, one run- intercoftales and lumbares fuperiores. ning upward, called vena cavafuperior; the other down- The two fubclaviae run laterally or toward each fide, ward, called vena cava inferior. and terminate as they go out of the thorax, between the The vena cava fuperior is diftributed chiefly to the firft rib and clavicula. thorax, head, and upper extremities, and but very lit- The right fubclavian, which is the (horteft of the two, tle to the parts below the diaphragm. commonly fends out four capital branches; the jugulaThe vena cava inferior is diftributed chiefly to the ab- ris externa, jugularis interna, vertebralis, and axillaris. domen and lower extremities, and but very little to the The left fubclarian being longer than the right, gives parts above the diaphragm. off, firft of all, the fmall veins on the left fide, anThe trunk of each of thefe two veins fends off, much fwering thofe on the right fide that come from the trunk in the fame manner with the arteries, a certain number of of the fuperior cava, viz. the mediaftina, pericardia, rincipal or capital branches, which are afterwards rami- diaphragmatica fuperior, thymica, mammaria iurerna, ed in different manners. Each trunk terminates after- and trachealis. wards by a bifurcation or a divifion into two fubordinate Next to thefe fmall veins, called finiflrce, it detaches trunks, each of which gives off other principal branches, another mall branch, called intercofalis fuperior fnifending in a great number of fmall trunks, rami, and ra- tra, and then four large branches like thofe from the riiifications. right fubclavian, viz. the jugularis externa, jugularis The fuperior vena cava runs up from the right auri- interna, vertebralis, and axillaris, which are termed ficle of the heart, almoft in a diredl courfe, for about two niftrae. fingers breadth, lying within the pericardium, in the The external jugular veins are diftributed chiefly to right fide of the trunk of the aorta, but a little more an- the outer parts of the throat, neck and head; and fend teriorly. a fmall vein to the arm, named cepbalica, which affifts As it goes out of the pericardium, it is inclined a lit- forming a large one of the fame name. tle to the left hand, and then runs up as high as the car- in The jugular veins go to ti e internal parts of tilage of the firft true rib, and a little higher than the the neckinternal and head, communicating with the finufts of Vol. I. No. 10. 3 3O the