168 THE CHEST. 



At the shoulder is a muscle of immense strength, and tendinous elastic composition, 

 the serratus major, spreading over the internal surface of the shoulder-blade and a 

 portion of the chest. A spring of easier play could not have been attached to the 

 carriage of any invalid. It is a carriage hung by springs between the scapulae, and 

 a delightful one it is for easy travelling ; while there is combined with it, and the 

 unionis not a little difficult, strength enough to resist the jolting of the roughest road 

 and the most rapid pace. 



Laterally there is sufficient defence against all common injury by the expansion of 

 the shoulder over the chest from between the first and second to the seventh rib ; and 

 behind and below that there is the bony structure of the ribs, of no little strength ; 

 and their arched form, although a flattened arch ; and the yielding motion at the base 

 of each rib, resulting from its jointed connexion with the spine above and its cartila- 

 ginous union with the sternum below. 



A still more important consideration with regard to the parietes of the thorax is the 

 manner in which they can adapt themselves to the changing bulk of the contents of 

 the cavity. The capacity of the chest is little affected by the external contraction 

 and dilatation of the heart, for when its ventricles are collapsed its auricles are 

 distended, and when its auricles are compressed its ventricles expand ; but with 

 reo-ard to the lungs it is a very different affair. In their state of collapse and expan- 

 sion they vary in comparative bulk, one-sixth part or more, and, in either state, it is 

 necessary for the proper discharge of the function of respiration that the parietes of 

 the chest should be in contact with them. 



The ribs are eighteen in number on either side. Nine of them are perfect, and 

 commonly called the true, or, more properly, sternal ribs, extending from the spine to 

 the sternum. The remaining nine are posterior and shorter, and are only indirectly 

 connected with the sternum. 



The ribs are united to the corresponding vertebraj, or bones of the spine, so as to 

 form perfect joints — or, rather, each rib forms two joints. The head of the rib is 

 received between the vertebra; and bones of the spine, before and behind, so that it 

 shall always present two articulating surfaces ; one opposed to the vertebra imme- 

 diately before, and the other to that immediately behind, and both forming one joint, 

 with a perfect capsular ligament, and admitting of a rotary motion. The head of 

 the rib seems to be received into the cartilaginous ligamentous substance between the 

 vertebra;. Nothino- could be more admirably devised for motion, so far as it is 

 required, and for st'rength of union, that can scarcely be broken. 



Before the ribs reach the sternum, they terminate in a cartilaginous prolongation, 

 or the lower part of the rib may be said to be cartilaginous. There is between the 

 bony part and this cartilage, a joint with a true capsular ligament, and admitting of a 

 certain degree of motionl and where it unites with the sternum, there is a fourth 

 joint, with a perfect and complete capsular ligament. 



The cartilages of the posterior ribs are united to the bony portion by a kind of joint. 

 They are not, however, prolons'ed so far as the sternum ; but the extremity of one lies 

 upon the body of that which is immediately before it, bound down upon it by a cellular 

 substance approaching to the tiature of ligament, yet each having some separate 

 motion, and all of them connected indirectly with the sternum, by means of tlie last 

 sternal rib. It is an admirable contrivance to preserve the requisite motion which 

 must attend every act of breathing, every extension and contraction of the chest, with 

 a degree of strength which scarcely any accident can break tlirough. 



The sternum, or breast-bone, is more complicated than it at first appears to be. It 

 constitutes the floor of the chest, and is a long flat spongy bone, fixed between the 

 ribs on either side, articulating with these cartilages, and serving as a point of sup- 

 port to them. It is composed of from seven to nine pieces, united tog(>ther by car- 

 tilage ; and whatever changes may take place in other parts of the frame, tliis cartilage 

 is not converted to bone,'even in extreme old age, although there may, possibly, be 

 some spots of ossific matter found in it. 



end of cartibfre only, the form of the arch could not have been sustained, but, sooner or later, 

 it must have^bent inward, and so have encroached upon the cavity of the chest as to have 

 compressed the organs of respiration and circulation to that degree that could not but have 

 ended in suflbcation and death of the animal. It was only ihe judicious and well-arranged 

 combination of bone and gristle in the construction of the chest that could answer the ends an 

 ail-wise Providence had in \\ew."— Veterinarian, vol. xv. p. 184. 



