LUNGS. 



hind thnn in tlie front : and hence arifcs the deep excavation 

 on each fide of the cheft, in the former direftion, for lodging 

 the lungs. They are all twifced on themfelves, fo that the 

 two extremities cannot rcil at the fame time in an horizontal 

 plane. The point of twilling is at the angle, coni'equently 

 the firll, which has no angle, does not exhibit this circum- 

 Ihmce, which is the more fenfible in proportion as the angle 

 is more ilrongly marked. The ribs are diftingnilhed into 

 two clafl'es : the feven fuperior ones, articulated to the fter- 

 num, are called Inw, or thoracic ; the five inferior, joined 

 to each other in front by their cartilages, which are not 

 connefted to the fternum, are named ya^, or abdominal. 

 Each is divided into a vertebral and a cartilaginous ex- 

 tremity, and a body. 



The vertebral extremity is pofleriorand articulated to the 

 fpine. It exhibits a rounded itnd contraftcd neck, of about 

 an inch in length, reiling on the tranlverfe procefs of the 

 correfpondiiig vertebra. Tliis neck is (lightly expanded at 

 its pofterior end, to form the head of the rib, which ex- 

 hibits a cartilaginous furface for articulation with tlie ver- 

 tebral cohimn. The fuiface is rounded in its outline, fingle 

 in the firft, eleventh, and twelfth ribs, v.'hich are each arti- 

 culated to a fingle body of a vertebra, and divided by a 

 rifing line into two parts in the nine others, which are fe- 

 verally articulated to hollaws formed between two vertebrsc. 

 Of thefe two portions the lower is the largeft. 



The cartilaginous extremity is elongated from above 

 downwards, broad and concave in the ten iirft ribs, and 

 narrower in the two lalt. It is moll clofely joined to the 

 correfponding cartilages, fo as to appear perfeftly con- 

 tinuous with it. 



The body of the rib may be confidered under four dif- 

 ferent points of view ; ii/z. the external and internal furfaces, 

 the fuperior and inferior margins. I. On the outfide it is 

 convex, and piefents behind a tubercle, marking the ter- 

 mination of the neck, and divided into two portions : the 

 inner of thefe is a fmooth cartilaginous furface, nearly cir- 

 cular in its figure, articulated to the tranfverfe procefs of 

 the lower of the two dorfal vertebrse, between the bodies of 

 •which the head is articulated; the external is rough, and 

 affords attachment to a ftrong ligament. This tubercle is 

 confounded with the angle in the firll rib, and is deficient 

 in the two laft. In front of this eminence is the angle, or 

 part at which the rib, after being continued from the ver- 

 tebral column obliquely downwards and outwards, turns 

 forwards : inflead of being angular, as its name implies, this 

 bend is gentle and i-ounded. It has a prominent oblique 

 line, not feen in the firft and twelfth, bijt flight in the fecond 

 and eleventh, and more Ilrongly marked and diftant from 

 the tubercle, in proportion as the rib is lower down : it gives 

 attachment to the facro-lumbalis. Between this angle and 

 the tuberofity there is a furface direfted backwards, oc- 

 cupied by the longitTimus dorfi, and becoming broader as 

 ■we trace the ribs from above downwards. The reil of the 

 rib, in front of the angle, forms a nearly fmooth furface, 

 direifted upwards in the firfl, where v.'e obferve in it two fu- 

 perficial iinprefnons made by the ccurfe of the fubclavian 

 arterv and vein, feparated by a furface, in which the fca- 

 lenus is inferted, and inclined more and more outwards in the 

 ■ fucceeding ribs, in proportion as they are lower. In the 

 middle of the fecond there is a mark from the attachment of 

 the ferratus anticus, and on the others analogous iniprc-ffions 

 from various mufclcs of the cheft and abdomen, as the ob- 

 Jiquus extemus, pedtoralis minor, furratus anticus, ferrati 

 poltici, &c. 



2. On the inlide the furface is uniformly concave and 

 fmooth, covered by the pleura, diretted downwards in the 



firft, a little inclined in the fame direftion in the fecond, but 

 completely internal in the remainder. 



J. Above, the body of the rib forms an obtufe margin, 

 which is internal in the firft, inclined upwards in the fecond, 

 and direftly fuperior in all the others. It affords attach- 

 ment to the intercoftal mufcles, except in the firft rib. 



4. The inferior margin is (harp, particularly near the tu- 

 bercle, and becomes more obtufe in front. Juft within this 

 is found the groove of the rib, which is deep at the back 

 part of the bone, becomes gradually fhallowcr, and is in- 

 fenfibly loll in the front. It lodges the intercoftal nerves, 

 but is hardly perceptible in the firft and laft ribs. This 

 inferior margin affords attachment to the intercoftal mufcles. 

 Thefe bones are thin in coinpaiifon to their length, and 

 have confiqiicntly coi fideri-.ble elafticity, which is not ob- 

 ferved in any 01 her part of the fl<eleto;i. They are com- 

 pofed moftly of compaft bone, with a little cellular ftruc- 

 ture in their centre : the latter is more abundant at the 

 anterior and polterior extremities. They are developed at 

 an early period in the foetus, and are more perfeft at the 

 time of birth than any other bones, except thole belonging 

 to the organ of hearing. They are formed from a fingle 

 point of olTification, excepting the head, which is not con- 

 folidated to the body till the formation of the flccleton is 

 ircarly complete. 



Sometimes there are thirteen ribs: the thirteenth may 

 be either above or below the ordinary feries. 



Art'iculalwris of the Chejl — The cheft, formed by bones of 

 an arched figure, moll of which reft on the fternum by one 

 end, and by the other on the vertebrx, prefents in front 

 and behind articulations correfponding to thefe relations. 

 The joints, feparately confidered, do not admit of much 

 motion ; but the pettoral cavity, taken altogether, enjoys 

 an extenfivc power of movement. 



The pojlenor ylriuvlations of the Cheji. — The ribs are united 

 to the vertebrte ; ill, by the articular furfaces of their 

 heads to the cavities in the bodies of the vertebrx, each of 

 which cavities is formed in a fingle vertebra for the firft, 

 eleventh, and twelfth, in the two adjoining bones and their 

 connefting fibro cartilage, for the other ribs ; 2dly, by 

 the articular furfaces of their tubercles to the tranfverfe pro- 

 ceffes of the vertebras, excepting the two laft ribs, which 

 have not this kind of articulation. The firft has been 

 called the cofto-vertebral ; the latter the cofto-tranfverfal 

 articulation. 



Tiw cojh-ij.'ricbral]omt%. In each of thefe the union is 

 effecled by means of an anterior and an inter-articular hga- 

 ment, and two fm,all fynovial membranes. The anterior 

 ligament is a broad, thin, flattened, and irregularly quadri- 

 lateral fibrous fafciculus, attached in front, above and be- 

 low the articular furface of the head of the rib, diverging 

 tov.ards the fpine, and fixed by its fuperior fibres to the 

 body «f the vertebra that forms the upper part of the 

 correfponding cavity, by its inferior to that which forms 

 the lower, and by tlie middle to the intermediate fibro- 

 cartil;ige. The latter are in general Itfs fenfible than the 

 two former, each of which forms a very diftindl fafciculus. 

 The difpofition of this ligament is not exactly the fisme 

 in the firft, eleventh, and twelfth ribs, each of which is ar- 

 ticulated to a fingle vertebra ; yet the fibres extend a little 

 on the neighbouring vertebras. It is covered in front by 

 the great lympatlietic nerve, by the pleura, and on the riglit 

 fide by the vena azygos : it has a radiated figure, is fhort 

 and ftrong, compoied of longer fupcrficial and fhorter 

 deep-feated fibres, and lias fmali vafcular intervals. It is ap- 

 plied over the joint, for wliich, in ccnjundion with the 



middle ' 



