1022 



THORAX. 



of the passions of his mind, while in the lower 

 animals we see none of these. 



OF THE THORAX IN MAN. Anatomy of the 

 framework of the Thorax. A portion of the 

 spine, the ribs, the sternum, together with 

 numerous muscles, form the wall of the human 

 thorax. The framework of bones is so ar- 

 ranged as to admit of free mobility in various 

 directions, so as to increase or diminish the 

 cubic capacity of the thoracic cavity. 



OftheDorsal Vertebrte. That portion of the 

 spine which enters into the composition of 

 the thorax consists of the dorsal vertebra?, 

 which are 12 in number, intermediate in size 

 and position, between the cervical and the 

 lumbar vertebra?. They form the main pillar 

 of support for the whole respiratory apparatus 

 the great fixed point for the chief respira- 

 tory muscles to act against or draw upon. 

 Their general appearance is that of increasing 

 in size from above downwards ; but when 

 carefully examined, they are as two cones, the 

 apices of which touch at about the fourth 

 or fifth vertebra, from which point, in either 

 direction, they increase in their dimensions ; 

 their breadth laterally exceeds their depth 

 from before backwards. Their bodies are large 

 and project deeply into the cavity of the tho- 

 rax, diminishing greatly the antero-posterior 

 diameter of the chest. Out of twenty cases, 

 the average projection is 2f of an inch, leaving 

 little more than 4 inches for the heart and 

 great blood-vessels. 



A deep sulcus is thus formed, which if 

 a cast be taken of the cavity of the thorax, 

 is very striking. In phthisis pulmonalis, 

 the space between the bodies of these verte- 

 brae and the sternum is sometimes /ew than one 

 inch ! When the thorax changes its form by 

 disease, this centre pillar is liable to wedge in 

 or jam up the thoracic organs against the walls 

 of the chest. 



The vertebrae are connected to each other 

 by ligaments, and jointed beautifully into each 

 other, so as collectively to admit of extensive 

 motion, while there is but little movement 

 between any two vertebrae. 



Of the bonds of union, the most remarkable 

 are the inter-vertebral disks (ligamenta inter- 

 vcrtebralia Weitbr.) composed of fibro- car- 

 tilage, and placed between the bodies of the 

 vertebrae, each disk serving to unite two 

 vertebrae, and yet to permit a motion in any 

 direction, yielding on that side towards which 

 the column inclines, while on the contrary side 

 it expands with the increasing intervertebral 

 space. This substance is to the brain what 

 the cushion or " buffer " between each railway 

 carriage is to the traveller; it breaks a sud- 

 den jar from being transmitted from carriage 

 to carriage. So does this intervertebral sub- 

 stance soften down any sudden jerk received 

 at the lower extremity of the spine, preventing 

 its being transmitted to the brain in the varied 

 actions of walking, running, and leaping. 



Of the Sternum (os pectoris : Xiphoides), so 

 named from aTtpvor, the breast : is a kind of 

 flattened bone, symmetrical in shape, which 

 occupies the anterior and middle part of the 



thorax. It is supported by the ribs on either 

 side ; it is broadest at its upper part, and 

 then narrowed ; it widens again, and finally 

 becomes compressed and narrow where it 

 joins the ensiform cartilage. (Fig. 660, e.) 

 Its direction is oblique from above down- 

 wards and forwards. This, with the curva- 

 ture backwards of the spine opposite to it, 

 increases the antero-posterior diameter of the 

 thorax, as may be seen in a lateral view of a 

 cast of the thoracic cavity. 



The length of the sternum, which is pro- 

 portionably smaller in the female than the 

 male, varies from 5 to 7 inches. At the 

 upper part its breadth is from li to 2 inches. 



Its thickness above is about 6 lines ; at its 

 lowest part it is much thinner, never exceed- 

 ing three lines. The ancients compared the 

 sternum to the sword of a gladiator ; and 

 hence have arisen the denominations given to 

 its various parts : as the handle (manubrium), 

 the body (mucro\ the point, or xiphoid 

 appendix, (ensiformis) ; but the last mention- 

 ed part now only retains the designation 

 grounded on this circumstance. This division 

 of the bone into three parts has been retained 

 by some modern anatomists, who describe the 

 three pieces of the sternum separately, as so 

 many distinct bones ; we shall only adhere to 

 this in speaking of the development of the 

 bone. 



In anatomical language it is said, the ster- 

 num presents two surfaces, two borders, and 

 two extremities. 



Of the anterior or cutaneous surface of the 

 Sternum. This is subcutaneous, slightly con- 

 vex and affords attachment to the aponeurosis 

 of the pectoralis major and the sterno-cleido- 

 mastoid muscles. It presents three orfourtrans- 

 verse projecting lines, which are traces of the 

 original division of the bone into five pieces. 

 The union between the 1st and 2nd pieces cor- 

 responds to the insertion of the 2nd costal car- 

 tilage, and is frequently cartilaginous even in 

 the adult age. The line which marks the union 

 of the first two pieces of the bone is the most 

 remarkable : it causes a projection of variable 

 size in different individuals, which has been 

 sometimes mistaken for a fracture or exos- 

 tosis. At the lower part we sometimes find a 

 foramen ; sometimes in place of the foramen 

 there is a considerable aperture, to which 

 much importance has been attached, as afford- 

 ing a proof of the primitive separation of the 

 bone in the median line. (Fig. 660. d.) The 

 existence of this opening explains how puru- 

 lent matter deposited behind the sternum 

 may, in certain cases, make its way outwards 

 without any absorption of the bone. This 

 bone is covered by a strong interlacement of 

 very numerous aponeurotic fibres. 



Of the posterior (mediastinal or cardiac) sur- 

 face. This is slightly concave, and parallel in 

 direction to the anterior surface. The con- 

 cavity is directed downwards and backwards, 

 towards the cavity of the thorax, and gives 

 attachment superiorly to the sterno-hyoidcits 

 and sterno-thuroideus muscles, inferiorly to the 

 triangularis sterni. 



