Page [unnumbered]
THE TWENTY-FIRST TABLE.
SHEWS the Sternum Rais'd, and the Principal Organs contain'd in the Thorax partly in View. A, The Inner-Face of the Sternum or Os Pectoris.
B B, The Cartilages of the True Ribs, cut from the Bony Extremities of the Ribs, and left at their Con∣nexions to the Sternum: Upon these Cartilages are plac'd the Musculi Triangulares; which Muscles Arise from the Inferior and Internal Part of the Sternum, and after an Oblique Progress are inserted to the Bony Endings of the Fourth, Fifth, Sixth, and sometimes Seventh, and Eight Ribs. These Triangular Muscles scarcely appear in Macilent Subjects, as is Exprest in this Figure.
C, The Mediastinum free'd from the Os Pectoris, where, in Humane Bodies it appears Double, being a Continuation of the Pleura from both Sides the Internal Part of the Thorax; whence it Descends and firmly Cleaves to the Pericardium, dividing the Thorax into Two Cavities, and the Right Lobes of the Lungs from the Left: In this Progress of the Mediastinum it parts with One of its Laminae to cover the large Blood-Vessels within the Thorax. A Triangular Interstice is fram'd immediately under the Sternum at the Approach of the Pleura, from each Side as it Descends to compose the Mediastinum: Nor is this Interstice an empty Space as it is commonly suppos'd, but is interwoven with various Orders of Fibres, framing Loculi or little Cells. Real. Columbus Lib. xi. Cap. iii. Proposes the letting out of Pus, collected in this Interstice by Perforating the Sternum. As the Fore-part of the Mediastinum plainly appears a Continuation of the Pleura•• so its Back-part is evidently a Continuation of the same Membrane, as it advances towards the Vertebrae of the Back. In Dissecting a Morbid Body, I found the Right Side of the Ca∣vity of the Thorax so extended with a Serous Humor, as its External Appearance, (especially at the Cartilaginous Endings of the True Ribs,) was Prominent: Nor would the least Portion of the Lungs on the same Side Swim in common Water, but Sunk to the Bottom of the Vessel: In this Subject I could not find any Part of the Hydropick or Serous Humor in the other Side of the Thorax; but the Lungs on that Side in no very ill State. By this, we may be assur'd that the Mediastinum ade∣quately divides the Right Side of the Thorax from the Left. The Mediastinum also supports the Pericardium, leaft its Flacci∣dity impede the Systole of the Heart, and sustains the Trunks of the Nerves of the Par Vagum in their Progress thro' the Tho∣rax. The Diaphragm is also said to be suspended by the Mediastinum, leaft the Liver, to whose Lower-Side it's Connexed, should become Insupportable. The Mediastinum receives Arteries from the Mammary and Intercostal Branches; it has Two large Veins which discharge their Blood into the Subclavian and Neighbouring Trunks: Its Nerves are said to Spring from the Eighth Pair. The Lymphe-Ducts of the Mediastinum pass towards the Thymus.
D D, The Pericardium or Capsula Cordis Open'd and Pinn'd up. The Pericardium Arises from the large Vessels at the Basis of the Heart, and seems to be compos'd of a Continuation of the Pleura or Mediastinum. It adheres to the Diaphragm below, and laterally to the Mediastinum. It has Blood-Vessels from the Diaphragm and Mammary-Vessels, according to the Accu∣rate Ruysch in his lately publish'd Epistles: The Capillary Extremities of these Blood-Vessels are very Numerous, as will appear when Injected with Mercury. There are divers Lymphe-Ducts on the Pericardium, which convey the Lympha to the Thora∣cick-Duct. The Glands, which are in the Pericardium and at the Basis of the Heart, which separate that Humor imploy'd in Moistening the Inside of that Membrane and Surface of the Heart, are not to be discover'd by the naked Eye in ordinary Dissections; no more than those on the Inside of the Peritonaeum and Surface of the Intestines, which afford a Humor to Lu∣bricate those Parts; but when either of these Parts are Diseased so that those Glands are Affected, their Existence then is De∣monstrable; as appear'd in the Pericardium of an Infant I lately Dissected, where the Neighbouring Parts and Pericardium its self were Apostumated. In the Pericardiums of this Subject we found Two or Three Ounces of Purulent Matter in place of the Serous Humor; and the External Membrane of the Heart so loosned, as its Surface appear'd Villous; nor did any Fat appear on the Basis of the Heart. In an Adult Person who Died suddenly I found the Pericardium somewhat Thickned and no Humor contain'd in it; but in Two, or Three Places cleaving to the Heart especially near its Basis, and the Heart it self intirely cover'd with Fat; The Use of the Pericardium is to defend the Heart in its Systole from the Neighbouring Parts, and to contain a Humor to Moisten the External Surface of the Heart.
E, The Heart lying within the Pericardium.
F F, Parts of the Lungs on both Sides the Thorax in Situ.
G, The Thymus in Situ. The Magnitude of the Thymas varies according to the Age of the Body; in a Faetus Two Months after Conception it is larger in Proportion to the Bulk of the Body than in One of Five or Six Months: In a Faetus of Nine Months it almost fills the Interstice which the Lungs after the Birth begin to take up in the Upper-part of the Thorax. The Thymus after the Birth gradually decreases, except the Upper-part of the Cavity in the Thorax is Capacious enough for its Reception, as appear'd in an Anatomical Subject I lately Dissected of Thirty Years of Age, in whom the Thymus was very large: I must confess I never yet met with a Subject, tho never so Old, in whom the Thymus was wanting. In those Bo∣di•••• the Thymus is less than ordinary, we find the Subclavian Glands, those of the Internal Jugular Veins, and the Glandule Thyraidam larger; as they lately appear'd in a Boy of about Eight Years of Age. In Women the Thymus and Thyroid Glands are larger than in Men, but the Subclavian Glands are less; by reason the Claviculae in Women are straight and shorter than those of Men; whence a much less Interstice is frain'd for entertaining those Glands. I have more than once found the Lymphe-Ducts fill'd with Wax, which Arise from the Thymus, and empty themselves into the Upper-part of the Thoracick-Duct; by Injecting that Duct by the Vesica Chyli: See App. Fig. 12. D.
From what has been abovesaid, it appears the Thymus bears a Proportion to the Head; whether in the Faetus or in Bodies before they become Adult, which we conceive, is in order to receive a Proportionable Quantity of Lympha, deriv'd from thence: And as the Subclavian Glands of Women are less than those of Men; so the Thyroide Glands and Thymus are larger: Hence also it appears the Thymus is a Lymphatick Gland, and Varies its Magnitude according to the Quantity of the Lympha, that is necessarily transmitted thro' it from the Superior Parts; or as the Neighbouring Lymphatick Glands do more or less transmit their Lympha to it: Besides this common Office of the Thymus, whether in the Faetus or Adult; it has another Use which was first suggested to Me by Injecting a Liquid into the Thoracick-Duct; when finding it not only fill the Lymphe-Ducts of the Thymus, but the Thymus it self was Extended with it: The like Observation, I since found, was made by the Expert Ana∣tomist Dr. Tyson, some Time since; whence I conceive, the Thymus and its Lymphe-Ducts are Diverticula to the Chyle, when too great a Quantity is pressing forewards towards the Subclavian Vein. I know it may be Objected that the Valves of the Lymphe-Ducts oppose this contrary Course of Liquours in them; but repeated Observations convince me, that not only these Lymphe-Ducts of the Thymus, which are large and have very few if any Valves, (as appears by their being Injected with Wax) but those of the Loins, and their Glands from whence they Arise, are frequently fill'd with Chyle, when no Compress is made on the Thoracick-Duct. Hence it is, a Milky Liquor has been commonly found in the Thymus, but more frequent in that of a P••tus than i•• an Adult; and that not only because the Thymus and its Lymphe-Ducts are much larger Proportio∣nably in the former State or Faetus, but the bended Position of the Thoracick-Duct of the Fetus in Vter••, renders the Ascent of the Chyle by that Duct more liable to Regurgitate by the Lymphe-Ducts of the Thymus.
H H, The Fore-part of the Diaphragma free'd from the Cartilaginous Endings of the Ribs, and Pinn'd up.