RIBS. 11T 



their breadth is more considerable in front than behind, and between the upper 

 than between the lower ribs. The ribs increase in length from the first to the 

 seventh, when they again diminish to the twelfth. In breadth they decrease from 

 above downwards ; in each rib the greatest breadth is at the sternal extremity. 



Common characters of the Ribs (fig. 75). Take a rib from the middle of the 

 series in order to study its common characters. Each rib presents two extremities, 

 a posterior or vertebral, an anterior or sternal, and an intervening portion, the 

 body or shaft. The posterior or vertebral extremity presents for examination a head, 

 neck, and tuberosity. 



The head (fig. 76) is marked by a kidney-shaped articular surface, divided by 

 a horizontal ridge into two facets for articulation with the costal cavity formed 

 by the junction of the bodies of two contiguous dorsal vertebras ; the upper facet 

 is small, the inferior one of large size ; the ridge separating them serves for the 

 attachment of the interarticular ligament. 



Fig. 76. Vertebral Extremity of a Eib. External Surface. 



Jcr AntT. Cntto-tTH.iisL^g.. fyr pvst* Cutto-tranivcTre Liy* 



Facet fur lodti of tipper Dorsal Vertebra 



Jitdijc frr fnler-articular Liy 

 facet for lof/y of 2ave-r Dorsal V^rt- 

 for tra.iuv.yroe. of I 



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 transverse process of the lower 

 of the two vertebra 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- 

 transverse 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 ; 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-arti- 

 cular portion is a rough elevation, which affords attachment to the posterior costo- 

 transverse 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 external 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 between 

 the angle and the tuberosity increases gradually from the second to the tenth rib. 

 The portion of bone between these two parts is rounded, rough, and irregular, and 

 serves for the attachment 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 its sternal extremity, an oblique line, the 

 {interior angle. The internal surface is concave, smooth, directed a little upwards 



