THE THORAX. STERXUM. 



23 



arrangement named by Owen the " typical vertebra " is completed by the addition 

 to the parts now mentioned of a pair of hcemapophyses and a hcemal spine, situated 

 in front of the centrum, as the neurapophyses and neural spine are placed behind ; 

 but in the thorax, according to his views, the .haemapophyses are supposed to be 

 transplanted to the extremities of the pleurapophyses, and form the costal cartilages, 

 carrying with them the sternum or series of haemal spines. 



However 'interesting these views may be, and however expedient the adoption in 

 Comparative Anatomy of some such words, expressive of anatomical relations, 

 more especially when it shall appear that the doctrines suggesting the terminology 

 are sufficiently established ; yet, as these are still imperfect, and as the names 

 by Avhich most parts of the human body are commonly designated have been long 

 in use, and are very generally understood, it seems premature for the present 

 to attempt a theoretical reformation of the nomenclature of human descriptive 

 anatomy. 



II. THE THORAX. 



The parts -which enter into the construction of the thoracic part of the 

 skeleton are the dorsal vertebrae already described, the sternum, the ribs, 

 and the costal cartilages. 



THE STERNUM OR BREAST-BONE. 



The sternum (os pectoris, os xiphoides) is situated in the median line at 

 the fore part of the thorax, in a sloping position, inclined downwards and 

 forwards. It is connected with the rest of the trunk by the costal cartilages 



Fig. 21. 



Fig. 21. THE STERNUM OP A MIDDLE-AGED . ,, 



MAN. I m " *^ n 



A, from before, 1, 2, 3, 4, 5, 6, & 7, the 

 articular surfaces for the corresponding costal 

 cartilages; 8, manubrium or upper piece, still 

 slightly separate from the body ; 9, middle 

 of the body ; 1 0, ensiform portion, osseous, 

 and united to the body; 11, inter-clavicular 

 notch ; 1 2, articular notch for the clavicle, 



B, the same sternum viewed from the 

 right side, showing the general convexity of 

 the bone forwards. The different facets of 

 articulation of the clavicle and costal carti- 

 lages will be distinguished by their position 

 in comparing the figure B with A. 



of the seven highest pairs of ribs, and 

 gives attachment to the clavicles. It 

 consists originally of six segments. 

 The first of these usually remains 

 distinct up to middle life, and is 

 called the manubrium ; the succeed- 

 ing four are united into one in the 

 adult, and form the body ; the sixth 

 generally remains cartilaginous up 

 to the period of puberty, and some- 

 times partially so even to advanced age, and is called the xiphoid, or 

 ensiform process, or cartilage : in middle life it is most frequently ossified 

 and united by bone to the body. 



The sternum is flattened from before backwards, and presents a slight 

 vertical curve with the convexity in front. It is of unequal width, being 



