76 SPECIAL ANATOMY. 



4. The eleventh and twelfth ribs, Costas fluctuantes very moveable ; 

 marked curve. Cullum, Tuberculum, et Sulcus, wanting. On the Capitulum 

 only one flat articular surface. Anterior extremity very thin and pointed. 

 The eleventh is longer. 



The costal cartilages are flat like the ribs, chiefly formed as these, and ossi- 

 fying easily upon the surface. They are twenty-four, sometimes twenty-six, 

 or only twenty-two. 



The external extremity lies in the fossa at the anterior termination of the 

 rib, the internal is either immediately united with the Sternum, in the true 

 ribs, or with the inferior border of the rib above, as the eighth to the tenth 

 costal cartilages, or extends freely into the abdominal walls, eleventh to the 

 twelfth. The borders of the fifth to the seventh ribs are united together. The 

 three superior are straight ; the rest curve outwards. Length : the first rib 

 is very short and thick, often ossified ; the following to the seventh always 

 longer ; from the eighth to the twelfth always shorter ; the twelfth only a few 

 lines long. In general, the length of the cartilage measures one-fifth of that 

 of the entire rib. 



Structure of the ribs : it is similar to that of the flat bones generally. 



Development : Ossification commences with the second month 

 of foetal life, from the body outwards. The osseous nuclei in the 

 capitulum and tuberculum appear only in the sixteenth year, and 

 completely united in the twenty-fifth year. 



86. External surfaces of the Chest. 



1. Anterior region, much broader below than above, inclining from behind 

 forwards, from above downwards. In the centre sternum, laterally the 

 costal cartilages with the intercostal spaces ; externally on either side the 

 linea chondro-sternalis, behind this the limit, namely the line of the anterior 

 angles. 



2. Lateral regions, more convex behind than before, presents the central 

 piece and the interspaces of the ribs. Intercostal spaces : these decrease in 

 breadth from above down wards ; however, the two last are broader than 

 those in the centre ; and the space between the anterior is broader than be- 

 tween the posterior extremities of the ribs. 



3. Posterior region, between the posterior angles. In the centre : 12 Proc. 

 spinosi dorsal f close to these the sulci vertebralis , 12 Proc. transversi ; the 

 articular connections with the tubercles. 



87. Cavity of the Chest, Cavitas thorads. 



Anterior wall ; concave, breast bone : costal cartilages. Posterior wall ; in 

 the centre : the projecting column of the vertebral bodies ; at the excavated 

 sides, fossae pulmonales, for the convex posterior surfaces of the lungs ; pos- 

 terior terminations of the ribs. 



Lateral parieties, formed by the ribs. 



Inferior wall, formed by the diaphragm. 



Superior wall wanting; in place of it, an oblique opening inclining from 

 above and behind downwards, for Trachea, (Esophagus, ductus thoracicus, 

 the great cervical and brachial vessels, nerv. vagus and phrenicus, the apex of 

 the lungs, several muscles. 



