OSTEOLOGY. 57 



they are not included in the class " long round bones." 

 Each rib presents a body and an upper extremity. The 

 extremity is divided into head, connected to the rest of the 

 bone by the nech, and tubercle. The head is a more or less 

 spherical process, with two convex, synovial, articulatory 

 surfaces, separated by a roughened groove. The anterior 

 surface articulates with the posterior facet on the body 

 of- the vertebra in front ; the posterior, with the anterior 

 facet of the vertebra behind ; the groove corresponds to the 

 intervertebral disc of cartilage and affords attachment to 

 ligamentum teres. Around each of the articulatory sur- 

 faces is a slight groove for attachment of a capsular liga- 

 ment. In the two last ribs the posterior articulatory 

 surface is continuous with the facet of the tubercle. The 

 neck varies in thickness and rotundity in the different 

 ribs ; its inner surface is roughened for attachment of the 

 stellate ligament. The tubercle seems to be the superior 

 part of the body, and is posteriorly placed to the head. 

 That of the first rib is largest ; it gradually decreases in 

 size in the bones from before backwards, so that it is ex- 

 tremely small in the two last. From this process arises 

 levator costse, and to it is attached longissimus dorsi. It 

 presents on its internal surface, becoming more anteriorly 

 placed in the posterior vertebras, a small articulatory facet 

 for union with the transverse process of the dorsal verte- 

 brae ; the outer circumferent margin of this is rough for 

 attachment of the capsular ligament, and on either side 

 for the costo-trans verse ligaments. The body is more or 

 less flattened irregularly from without inwards, and in the 

 central ribs is so twisted upon itself that the two extremi- 

 ties will not rest upon a plane surface at the same time. 

 The eighth rib takes the following course from its upper 

 extremity : at first, outwards, backwards, and downwards ; 

 centrally, more directly downwards ; inferiorly slightly 

 inwards and backwards. The body therefore presents two 

 margins and two surfaces. The internal surf ace is smooth, 

 convex from before backwards, concave from above down- 

 wards. It is covered by the pleura costalis, through which 

 it may be seen on laying open the thorax of a fresh sub- 

 ject. At its extreme superior part the sympathetic gan- 

 -gliated cord may be seen. To the extreme inferior part of 

 this surface of the posterior ribs are attached the diaphragm 

 .and transversalis abdominis. The external surface is convex 



