Thorax 51 



typical arrangement. Head rounded, with a singh facet for the first dorsal body, 

 neck elongated, tubercle pronounced, no angle. Upper surface marked by scalene 

 muscles and structures passing between them to axillary sheath, showing from behind 

 forwards a rough area for Scalenus medius in front of the tubercle, a groove for sub- 

 clavian artery (or first dorsal nerve, or both), a scalene tubercle near inner margin for 

 Scalenus anticus, and a shallow groove at anterior end for subclavian vein. The partly 

 calcified shell of the costal cartilage is frequently attached to the bone, causing it to 

 appear longer than usual. There is no subcostal groove. The whole bone is more or 

 less in one plane, though the head and neck sometimes show a little downward curve 

 not upward, as in the lower bones. 



Second Rib. Surfaces look more upward and downward than outward and 

 inward : in fact, the bone has somewhat the appearance of a much elongated edition 

 of a first rib. Head has two facets, the upper one very small. Said sometimes to have 

 no angle, but this is not a true description of most bones : angle a short distance from 

 tubercle. A prominent boss of bone about half-way round the outer side of shaft for 

 origin of Serratus magnus. Subcostal groove very broad on hinder part of shaft. This 

 rib also, like the first, lies more or less in one plane. 



Tenth Rib. Head may have one or two facets, according to the individual articula- 

 tion, with the tenth dorsal vertebra only, or with the ninth and tenth. Tubercle may 

 have a definite though small articular facet, or this may be absent. 



Eleventh and Twelfth Ribs. These do not articulate with transverse processes 

 so they do not present tubercles : they are only carried by their corresponding vertebral 

 bodies, so their heads have single facets. The eleventh rib is longer than the last, 

 shows a definite angle, and has a trace of subcostal groove : the last rib has neither 

 tubercle, groove, nor angle, and varies in length from i to 7 or 8 inches. Each of these 

 ribs carries a free pointed short cartilage, embedded in the deeper layers of the abdominal 

 wall 



For the detailed examination of ribs and cartilages it will be well to take a middle 

 rib and work out on it the various parts and markings, and then to follow the modifi- 

 cations of these that occur as one passes towards the ends of the series. 



Examine first the vertebral end of such a rib (Fig. 42). Roughnesses are found 

 round its articular surfaces for ligamentous bands connecting it with the vertebral 

 bodies. These bands are best developed in front, where they form the " stellate " 

 ligament : this is described as having upper, middle, and lower parts diverging to the 

 two vertebral bodies and intervertebral disc which carry the rib-head, but the division is 

 usually indistinct. The interarticular band is thin, separating the two articular 

 cavities, and is probably derived from the upper fibres of the capsule, left in situ when 

 the articular surface extends to the upper vertebra from the lower, to which it properly 

 belongs. 



Looking at the inner end of the bone from the front, it is found to present two areas 

 at its vertebral end, the lower of which (P) is pleural and directly continuous with the 

 pleural surface of the shaft : the upper area (X) is confined to the neck and shaft 

 between the neck and angle, and is separated by a soft fatty tissue from the membrane 

 which supports the pleura. The intercostal vessels and nerve run through this tissue 

 in front of the upper costo-transverse ligament (the nerve is shown in the figure), but 

 do not come into contact with the bone until they get near the angle. The depth of 

 X depends on the growth of the Crista colli superior. The " endothoracic fascia, " 



42 







