162 



SPECIAL ANATOMY OF THE SKELETON 



space is called an intercostal space (spatium intercostale). The length of these 

 spaces corresponds to the length of the ribs and their cartilages; their breadth 

 is greater 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 downward; in the 

 upper ten the greatest breadth is at the sternal extremity. 



Common Characters of the Ribs. A rib from the middle of the series 

 should be taken in order to study the common characters of the ribs (Figs. 129 

 and 130). Each rib presents two extremities, a posterior or vertebral, an anterior 

 or sternal, and an intervening portion the body or shaft. 



Posterior Extremity. The posterior or vertebral extremity presents for examina- 

 tion a head, neck, and tuberosity. 



The head (capitulum costae) (Fig. 130) is marked by a kidney-shaped artic- 

 ular surface, divided by a horizontal ridge (crista capituli) into two facets for 



Articular part of tubercle 

 Nonarticular part of tubercle 



Demifacet for vertebra 



Interarlicular crest 



Demifacet for vertebra 



Subcostal groove 



FIG. 130. A central rib of the left side, viewed from behind. 



articulation with the costal cavity formed by the junction of the bodies of two 

 contiguous thoracic vertebrae; the upper facet is small, the inferior one of larger 

 size; the ridge separating them serves for the attachment of the interarticular 

 ligament. 



The neck (collum costae) is that flattened portion of the rib which extends out- 

 ward from the head; it is about an inch long, and is placed in front of the trans- 

 verse process of the lower of the two vertebrae with which the head articulates. 

 Its anterior surface is flat and smooth, its posterior surface is rough for the attach- 

 ment of the middle costotransverse ligament, and is 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 border presents a rough 

 crest (crista colli costae} for the attachment of the anterior costotransverse liga- 

 ment; 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. 



The tuberosity (tuberculum costae) consists of an articular and a nonarticular 

 portion. The articular portion (fades articular is tuberculi costae), the more in- 

 ternal and inferior of the two, presents a small, oval surface or articulation with 

 the extremity of the transverse process of the lower of the two vertebra? to which 

 the head is connected. The nonarticular portion is a rough elevation, which 



