THE RIBS. 



195 



(Fig. 143) is marked by a kidney-shaped articu- Fig. 142. A Central Bib of Eight 

 3ar surface, divided by a horizontal ridge into Side * Inner Surface, 



two facets for articulation with the costal cavity ^"*<v, 



formed by the junction of the bodies of two 

 contiguous dorsal vertebrae ; the upper facet is 

 small, the inferior one of large size; the ridge 

 separating them serves for the attachment of , 

 the inter-articular ligament. 



The neck is that flattened portion of the rib 

 which extends outwards from the head; it is 

 about an inch long, and rests upon the trans- 

 verse process of the lower of the two vertebras 

 with which the head articulates. Its anterior 

 surface is flat and smooth, its posterior rough, for 

 the attachment of the middle costo-transverse 

 ligament, and perforated by numerous foramina, 

 the direction of which is less constant than those 

 found on the inner surface of the shaft. Of its 

 two borders, the superior presents a rough crest 

 for the attachment of the anterior costo-trans- 

 verse ligament; its inferior border is rounded. 

 On the posterior surface of the neck, just where 

 it joins the shaft, and nearer the lower than the 

 upper border, is an eminence the tuberosity or 

 tubercle ; it consists of an articular and a non- 

 articular portion. The articular portion, the most 

 internal and inferior of the two, presents a small 

 oval surface, for articulation with the extremity 

 of the transverse process of the lower of the two 

 vertebrae to which the head is connected. The 

 non-articular portion is a rough elevation, which 

 affords attachment to the posterior costo-trans- 

 verse ligament. The tubercle is much more 

 prominent in the upper than in the lower ribs. 



The shaft is thin and flat, so as to present two 

 surfaces, an external and an internal ; and two 

 borders, a superior and an inferior. The exter- 

 nal surface is convex, smooth, and marked, at its 

 back part, a little in front of the tuberosity, by 

 a prominent line, directed obliquely from above, 

 downwards and outwards ; this gives attachment 

 to a tendon of the Sacro-lumbalis muscle, and is 

 called the angle. At this point, the rib is bent 

 in two directions. If the rib is laid upon its 

 lower border, it will be seen that the anterior 

 portion of the shaft, as far as the angle, rests 

 upon this margin, while the vertebral end of the 

 bone, beyond the angle, is bent inwards, and at 

 the same time tilted upwards. The interval be- 

 tween the angle and the tuberosity increases gra- 

 dually from the second to the tenth rib. The por- 

 tion of bone between these two parts is rounded, 

 rough, and irregular, and serves for the attach- 

 ment of the Longissimus Dorsi. The portion of 

 bone between the angle and sternal extremity is 

 also slightly twisted upon its own axis, the external surface looking downwards 

 behind the angle, a little upwards in front of it. This surface presents, towards 



