Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/270

 226 ' ANATOMY. Part Ilf. The arteria pulmonalis carries the venal blood through Thefe capital branches or arteries are for the moft part all the capillary veffels of the lungs. difpofed in pairs ; there being none in odd numbers but Both thefe great or general arteries are fubdivided in- the caeliaca, the two menfentericae, fome of the oefophato feveial branches, and into a great number of ramifi- gaeae, the bronchialis, and fometimes the facrce. cations. ■ In this part, we ftiall defcribe the diftributions The aorta gives rife to two fmall arteries, called cqof the aorta, leaving the pulmonary artery to the parti- ronariae cordis, which go to the heart and its auricles; cular hiftory of the lungs. See Part VI. one of which is fituated anteriorly, the other pofteriorly, The bafis of the heart being very much inclined to the and fometimes they are three in number. fight fide; and turned a little backward, the aorta goes From the upper part of the arch or curvature, the aout from it in a direct courfe, nearly over-againfl the orta fends out commonly three, fometimes four large cafourth vertebra of the back. Its courfe is direct with pital branches, their origins being very near each other. refpedt to the heart; but with refpeft to all the 'reft of When there are four, the two middle branches are termthe body, it afcends obliquely from the left to the right ed arterise carotides; the ether two, fubclavias; and both are diftingUifhed into right and left. hand, and from before backward. Soon-after this, it bends obliquely from the right When there are but three branches, which is oftepeft hand to the left, and from before backward, reaching the cafe, the firft is a fhort trunk, common to the right as high as the fecond vertebra of the back; from whence fubclavian and. carotid, the fecond is the left fubclavian, it runs down again in the fame direction, forming an ob- and the third the left carotid. lique arch. The middle of this arch is almofi oppofite : The origin of the left fubclavian terminates the aorta to the right fide or edge of the fuperior portion of the afeendens. flernum, between the cartilaginous extremities or liernal The carptid arteries run up directly to the head, each articulations of the firlt two ribs. of them being firft divided into two, ope external, the oFrom thence the aorta defcends in a direfb courfe a- ther internal. The external artery goes chiefly to the long the anterior part of the vertebrae, all the way to the outer parts of the "head and dura mater, or firft covering -os facrum, lying a little toward the left hand; and there of the brain. The internal enters the cranium, through it terminates in two fubordinate or collateral trunks, cal- the bony canal of the os petrofum ; and is diftributed through the brain by a great number of ramifications. led arteriae iliacae. The aorta is by anatomifts generally divided into the The fubclavian arteries feparate laterally, and almoftaorta afeendens and aorta defeendens, though both are tranfverfely, each toward that fide on which it lies, bebut one and the fame trunk. It is termed afcendens, hind and under the claviculas, from whence they have .from where it leaves the heart to the extremity of the their name. great curvature or arch. The remaining part of this The fubclayian on each fide terminates at the upper trunk from the arch to the os facrum or bifurcation, al- edge of the firft rib, between the lower infertions. of the firft fealenus nrufcle; and there, as it goes out of the thoready mentioned, is named defeendens. The aorta defeendens is further divided into the fupe- rax, takes the name of arteria axillaris. rior and inferior portions; the firft taking in all that lies During this courfe of the fubclavian artery, feveral above the diaphragm ; the other all that lies between the arteries arife from it, viz. the mammaria interna,, mediaftina, pericardia, diaphragmatica minor five fuperior, diaphragm and the bifurcation. The aorta afeendens is chiefly diftributed to part of thymica and trachealk. T he thymica and trachealis on each fide are,, in fome the thorax, to the head and upper extremities. The fubjedts, only branches of one fmall trunk which fpring iuperior portion of the aorta defeendens furniflies the reft of the thorax • the inferior portion furnilhes the abdo- from the common trunk of the right fubclavian and carotid. men and lower extremities. The great trunk of the aorta, through its whole length, They are generally fmall arteries which run fometimes fends off immediately feveral branches, which are after- feparate, and fometimes partly feparate and partly joined. wards differently ramified ; and thefe arterial branches The fubclavian fends off likewife the mammaria intermay be looked upon as. fo many trunks with refpeft to na, vertebrales, cervicales, and fometimes feveral of the the other ramifications, which again may be confidered upper intercoftales. as fmall trunks with regard to the ramifications that they The axillary artery, which is only a continuation of fend off. the fubclavian from where it goes out of the thorax to The branches which go out immediately from the the axilla, detaches chiefly the mammaria externa, or trunk of the aorta, may be termed original or capital thoracica fuperior, thoracica inferior, fcapulares externae, branches; and of thefe fome are large and others very fcapularis interna, humeralis or mufcularis, <bc. Afterwards it is continued by different ramifications, and unfmall. The large capital branches of the aorta are thefe: der different names, over the whole arm, all the way to two artarias fubclaviae, two carbtides, one caeliaca, one the ends of the fingers. mefenterica fuperior, two renales, formerly termed e- The fuperior portion of the aorta defeendens gives off mulgents, one mefenterica inferior, and two ilxacas. the arteriae bronchiales, which arife fometimes by a fmall The fmall capital branches are chiefly the arteriae co- common trunk, fometimes feparate, and fometimes do ronarise cordis, bronchiales, cefophagaeae, intercoftales, dia- not pome immediately from the aorta. It next fends off phragmaticae inferiores, fpermaticae, lumbares, and faerse.. the oefophagaeae, which may be looked upon as mediaftinse pofteriores ;