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 278 ANATOMY. Part VI. The tubercle which lies in the center of the areola, is THYMUS. termed papilla, or the nipple. In women with child, or who give fuck, it is pretty large, and generally longer or The thymus is an oblong glandular body, round on the upper part, and divided below into two or three higher than it is thick or broad. The texture of the nipple is fpungy, elaftic, and liable lobes, of which that toward the left hand is the longeft. to divers changes of confidence, being fometimes harder, In the foetus it is of a pretty large fize, lefs in children, fometimes more flaccid. It feems to be made up chiefly and very little in aged perfons. of ligamentary fafciculi, the extremities of which form The greateft part of the thymus lies between the duplicature of the fuperior and anterior portion of the methe balls and apex of the nipple. Between thefe fpungy and elaftic fafciculi lie feven or diaftinum, and the great veffels of the heart; from whence eight particular tubes, at fmall diftances from each other, it reaches a little higher than the tops of the two pleuras, and ail in the fame direction. Thefe tubes end at the fo that fome part of it is out of the cavity of the thorax. bafis of the papilla in the irregular circle of communica- Its particular inward ftrudlure and fecretions are not as tion of the lactiferous dudts, and at the apex, in the fame yet fufliciently known to determine its ufes, which however feem to be defigned more for the foetus than for adults. number of almoft imperceptible holes or orifices-. The ufe of the mammae in the nourilhment of children is known to all the world: But it is not certainly known COR. what the papillae and areolae in males can be defignedfor. Milk has been obferved in them, in children of both The heart is a mufcularbody fituated in the cavity of the thorax on the anterior part of the diaphragm, befexes. tween the two laminae of the mediaftinum. It is in fome meafure of a conical figure, flatted on the fides, round PLEURA and MEDIASTINUM. at top, and oval at the bafis. Accordingly, we confidet The pleura is a membrane which adheres very clofely in the heart the bafis, apex, two edges, and two fides* to the inner furfaceof the ribs, fternum, and mufculi in- one of which is generally flat, the, other more convex, ter-coftales, fub-coftales, and fterno-coftales, and to the Befides the mufcular body, which chiefly forms what convex fide of the diaphragm. It is of a very firm texture, we call the heart, its bafis is accompanied by two appendices and plentifully ftored with blood-vefiels and nerves, in called auriculae, and by large blood-vcfiels ; all theft are incluied .in a membranous capfuia, named pericardium. all which it refembles the peritonaeum. The cellular portion goes quite round the inner fur- It is hollow within, and divided by a feptum which face of the thorax, but the membranous portion is difpo- runs between the edges into two cavities, called ventrifed in a different manner. Each fide of the thorax has culi, one of which is thick and folid, the other thin and its particular pleura, intirely diftimft from the other, and foft. This latter is generally termed the right ventricle, making as it were two great bladders, fituated laterally theothertheleft ventricle, though in their natural fituation with refpeCt to each other in the great cavity of the the right ventricle is placed more anteriorly than the left. bread, in fuch a manner as to form a double feptum or Each ventricle opens at the bafis by two orifices, one partition running between the vertebrae and the fternum, of which anfwers to the auricles, the other to the mouth iheir other fides adhering to the ribs and diaphragm. of a large artery ; and accordingly one of them may be This particular duplicature of the two pleurae is termed termed the auricular orifice, the other the arterial orimediaftinum. The two laminae of which it is made up fice. The right ventricle opens into the right auricle, are clofely united together near the fternum and vertebrae; and into the trunk of the pulmonary artery; the left, inbut in the middle, and toward the lower part of the fore- to the left auricle, and into the great trunk of the aorta. fde, .they are feparated by the pericardium and heart. At the edges of thefe orifices are found feveral moveable A little more backward they are parted in a tubular form pellicula;, called valves by anatomills ; of which forae are by the cefophagus, to which they ferve as a covering; turned inward, toward the cavity of the ventricles, called and in the moft pofterior part, a triangular fpace is left triglochines or tricufpides; others are turned towards the between the vertebrae and the two pleurae from above great veffds, called femilunaresor figmoidales. The valvulae downward, which is filled chiefly by the aorta. tricufpides of the left ventricle are likewife termed mitrales. The mediaftinum does not commonly terminate along The inner furface of the ventricles is very uneven, the middle of the infide of the fternum, but inclines to- many eminences and cavities being obfervable therein. ward the left fide. The moft confiderable eminences are thick fleftiy proThe furface of the pleura turned to- the cavities of the ductions called columnac. To the extremities of thefe bread, is continually moiftened by a lymphatic ferofit-y pillars are faftened feveral tendinous cords, the other ends which tranfudes through the pores of the membranous of which are joined to the valvulae tricufpides. There portion. are likewife other fmall Ihort tendinous ropes along both The pleura ferves in general for an inner integument edges of the feptum between the ventricles. Thefe fmall to the cavity of the thorax. The mediaftinum cuts off cords lie in an obliquely tranfverfe fituation, and form a all communication between the two cavities, and hinders kind of net-work at different diftances. ©ne lung from preffing on the other when we lie on one The cavities of the inner furface of the ventricles fide. It likewife forms receptacles for the heart, peri- are fmall deep fo flu lag or lacuna; placed very near each cardium, cefophagus, <&£.. other, with fmall prominent mterftices between them. The