132 THE SKELETON 



seventh cervical vertebra and had a radiate ligament. The tubercle was well developed, and 

 articulated with the transverse process. The costal cartilage blended with that of the first 

 thoracic rib, and gave attachment to the costo-elavicular ligament. Between it and the first 

 thoracic rib there was a well-marked intercostal space occupied by intercostal muscles. It 

 received the attachment of the scalenus anterior and medius muscles, and it was crossed by the 

 subclavian artery and vein. The nerves of the intercostal space were supplied by the eighth 

 cervical and first thoracic. The artery of the space w^as derived from the deep cervical, which, 

 with the superior intercostal, arose from the root of the vertebral. The head of the first thoracic 

 rib in this specimen articulated with the seventh cervical, as well as with the fii'st thoracic 

 vertebra. An interesting fact is also recorded in the careful account of this specimen. There 

 was no movable twelfth thoracic rib on the same side as this well-developed cervical rib, and the 

 twelfth thoracic vertebra had mammillary and accessory processes, and a strong elongated 

 costal process, and was in linear series with the lumbar transverse processes. 



Fig. 159. — Posterior Portion of the Sixth Rib in the Fifteenth Year. 



(After Toldt.) 



Epiphysis of non-articular portion of the tubercle 



Epiphysis of head 



Articular facet 



Gruber and Turner, from a careful and elaborate study of this question, summarise the varia- 

 tions in the cervical rib thus: — It may be very short and possess only a head, neck, and tubercle. 

 When it extends beyond the transverse process, its shaft may end freely or join the first thoracic 

 rib: this union may be effected by bone, cartilage, or ligament. In very rare instances it may 

 have a costal cartilage and join the manubrium of the sternum. Net unfrequently a process, 

 or eminence, exists on the first thoracic rib at the spot where it articulates with a cervical rib. 



Lumbar ribs are of less significance than cervical ribs and rarely attain a great length. 

 Their presence is easily accounted for, as they are the differentiated costal elements of the trans- 

 verse processes. They are never so complete as the cervical ribs, and articulate only with 

 the transverse processes; the head never reaches as far as the body of the vertebra, and there is 

 no neck or tubercle. An extra levator costce muscle is associated with a lumbar rib. 



Fig. 160. — Posterior Portion of the Sixth Rib in the Eighteenth Year. 



(After Toldt.) 



Non-articular portion of tubercle 



Epiphysis of head 



Epiphysis of the articular facet of the tubercle 



Not the least interesting variation of a rib is that known as the bicipital rib. This condition 

 i.s seen exclusively in connection with the first thoracic rib. The vertebral end consists of two 

 limbs which lie in different transverse planes. These bicipital ribs have been especially studied 

 in whales and man. This abnormality is due to the fusion of two ribs, either of a cervical rib 

 with the shaft of the first thoracic; or the more common form, the fusion of the first and second 

 true ribs. 



Among unusual variations of ribs should be mentioned the replacement of the costal carti- 

 lage and a portion of the rib-shaft by fibrous tissue, a process which occurs normally in the case 

 of the eighth rib during its development. 



Sometimes the shafts of two or more ribs may bocomf; united by small quadrilateral plates 

 of }>onc extending across the intercostal spaces. 



THE STERNUM 



The sternum (figs. IGl, 1G2) is a flat, oblong plate of bone, situated in the 

 anterior wall of the thorax, and divisible into three parts, called respectively — (1 ) 

 the manubrium sterni {'r)resternuui), (2) th(^ gladiolus (niesost(n-num), constitut- 

 fn^ the body of Uw. bone, and (8) tlic xiphoid (or onsiform) process (metasternum). 

 In the young subject it consists of six picuM^s or segment (sterneljr»). Ofthe.se, 

 the first remains separate throughout life and forms the manul)riuni; the sue- 



