LUNGS. 



ture, are difficultly reduced into gelatine by boiling, and 

 are remarkable for their tendency u> oHification. Kven in 

 fubje^s not much advanced in age, . we frequently tind a 

 bony point in the centre of thefe cartilages : this is the 

 commencement of olTirication. Thofe of the firll ribs un- 

 dergo this change mod readily : they are often com- 

 pletely bony, while the others (lill exhibit their natural tex- 

 ture. This ofTification is always preceded by a yellowifh 

 tint, which fuccceds to the white colour that characterizes 

 the cartilages of the child. When they are converted into 

 bone, they refemble the ribs in being compaft externally 

 and ceHular on tlie inlide. In the rib of an old perfon the 

 cells of the rib and of its cartilage are continuous. 



/Inu-iihitions of the CartUage! of the true Ribs. — Each of 

 thele has a finall, furface at its llernal extremity, received 

 into a correfpending hollow of the edge of the flernum, 

 covered by a thin layer of cartilage. The joint poireffes 

 an anterior and a polterior ligament, and a fynovial mem- 

 brane. The feventh rib is moreover united by a pecuhar 

 ligament to the enfiform cartilage. The anterior ligament 

 is thin and broad, compofed of radiated fibres arifingfrom 

 the extremity of the cartilage, diverging as they traverfe 

 the front of the articulation, and expanded on the front of 

 the flernum, where they are mixed with thofe of the oppo- 

 lite fide, with the periofteum, and with the fibres of in- 

 lertion of the peftoralis major, by which this ligament is 

 covered in front. The fiipcrficial fibres are long : the more 

 dceply-feated are fhorter, and proceed direftly from the 

 cartilage to the neighbouring portion of tlie flornum. They 

 are intermixed, not only with the oppofite fibre?, but alfo 

 with thofe of the ligament immediately above and below. 

 From tlie union of all thefe fibres a thick ftratum is formed, 

 covering and llrengthening the fternum, and more ftrongly 

 marked below than above. The pofterior ligament differs 

 from the preceding by being thinner and having its fibres 

 lefs apparent : in other refpefts they are neaiTy fimilar ; 

 that is, they proceed in a radiated manner from the car- 

 tilages to the llernum. The fibrous ftratum on this furface 

 of the bone Ls as thick as on the other, but it exhibits a 

 more uniform kind of organization. We do not fee in it 

 the dece.flation of numerous diftintf fafciciri, but a fmooth 

 and almod polifhed ftratum, adhering very clofely to the 

 bone, with many of its fibres not derived from the ligaments 

 of the ribs, but purfuing rather a longitudinal direftion. 

 The fynovial membrane is remarkable for its fmall extent, 

 and for the want of polifti on its furface. If we did not 

 difcern a fmall quantity of fynovia in the joint, we might be 

 inclined to doubt the cxiftence of fuch a membrane. In 

 this refpect it very much refembles that of the cofto-verte- 

 bral articulation. In general, it is rather more Irofe in 

 the two or three lower articulations, than in the fuperior 

 ones. In the adult it certainly does not esift in the firft : 

 the cartilage is continuous with the bone, which explains 

 the fmall amount of motion, of which this rib is fufcep- 

 tible. In the articulation of the fecond rib there is a fmall 

 inter-articular ligament. A finall elongated and very thin 

 fibrous faiciculus goes from the lower edgn; of the feventh 

 rib obliquely downwards and inwards to the front of the 

 enfiform cartilage, where it forms an angle with the ligament 

 of the oppofite fide. It is covered by the reftus ab- 

 dominis. 



j4rticulr.t'wtis of the CarttJages of the falfe Ribs. — We have 

 ftated, that the neighbouring edges of the fixth and feventh, 

 and of the feventh and eighth cartilages, are articulated by 

 means of oblong furfaces. Thefe are covered by fynovial 

 membranes much more apparent, more loofe, and containiH<T 

 snore fynovia. ;h!nv lUofe wbich are found between the fupe- 



rior cartilages and the fternum. Sometimea between the 

 fifth and fixth, more rarely between the eighth and ninth, a 

 fimilar articulation, and confequently a liniilar fynovial mem- 

 brane, are found, which manifeftly refer only to the mobi- 

 hty of thefe cartilages. To maintain the cartilages of the 

 falle ribs in tlleir pofitions, feveral ligamentous fibres, hold- 

 ing them llrongly, particularly in fi'oiit, pafs from the lalt 

 true to the firft faU'e rib ; from the latter to the fecond, and- 

 from it to the third. Thefe fibres arc particularly evident 

 in front of the lynovial membranes which we have mentioned. 

 Analogous fibres attach the extremity of each of the firft 

 three falfe cartilages to the lower portion of the cartilage 

 immediately above it. The only connediun of the two la(s 

 is by means of the mufcles. Ligamentous fibres alfo pafs be- 

 tween the cartilages of the fixth and feventh true ribs. 



The Chefl confidered in general. — We (hall arrange the de- 

 fcriptioii of this cavity under the divifions of its external and 

 internal furface ; fuperior and inferior circumference. The 

 external furface comprifes four regions ; an anterior or fter- 

 nal, a poilerior or vertebral, and two lateral or coftal. The 

 anterior is the narrowcll, more or lefs flattened or projecting 

 in different fubjetts, and according to the prevalence of 

 ccrtrnn prediipofitions. In the middle we have the cuta- 

 neous furface of the llernum, on the fides the cartilages of 

 the true ribs, and a feries of Imes, which indicate in each 

 rib the point of its union with the correfponding cartilage. 

 This feries may be conceived as united into one generaL 

 line, running obliquely from above downwards and from 

 wiihin outwards, forming the lateral boundary of the ante- 

 rior region, which, from this particular difpofition, is much 

 broader below than above. Between thefe cai-tiiages broad 

 intervals appear in the firft true ribs, narrower one* in the 

 laft : they are ftill more narrowed in the firil falle ribs, but 

 grow brcader again in the two laft of this elafs. 



The pofterior region prcfents the row of dorfal fpinous 

 proceffes ; the correfponding portions of the mufc'ular chan- 

 nels of the vertebrfe ; the tranlverfe procefies of the dorfal 

 vertebrae ; their articulations with the tubercles of the ribs ; 

 a feries of furfaces belonging to the latter, broader in pro- 

 portion as they are lower, comprehended between the tuber- 

 cles and the angles, and giving attachment to the longilfimus 

 dorfi ; and, laftly, a general line running obliquely from above 

 downwards and within outwards, formed by the feries o€ 

 angles of the ribs. The dillance between the angles and 

 the tuberofities increafing downwards, determines ihe obli- 

 quity of the linejufl mentioned, the increafing breadth of the 

 furfaces which it terrninates, and the form of this region, 

 which is of confiderable breadth below, and becomes nar- 

 rower as we trace it upwards. This difpofition is analogous 

 to that of the anterior region, where the cbliquity of the 

 lateral lines pi-oduces in the fame manner an inequality of 

 breadth. 



The lateral regions are convex, narrow above, and broader 

 below, formed by the ribs and the intcrcoilal intervals. 

 The latter are, in general, difpofed like the bones which 

 form them, but with fome varieties. 7^hey are fliort, and 

 broad above; then diminifh lucoeflively in breadth, and in- 

 creafe in length down to the jundlion of the two clafTes of 

 ribs ; after which, without growing broader, they again de- 

 creafe in length to the laft, which is very (hort : all of ihem' 

 are broader before than behind ; hence the dillance is much 

 greater between the anterior than the pofterior extremities 

 of the firft and laft ribs. Thefe fpaces are aU filled by the 

 intercoftal mufcles. 



The internal furface of the cheft, which lodges the prin- 



cipal organs of refpiration and circulatHjn, alfo offers four 



regions to our obfervation. The anterior entirely refembles 



ii that 



