CHAPTER VII. 



THE STERNUM. 



The Stemiun of Mammals is a bone, or generally a series 

 of bones, placed longitudinally in the mesial line, on the 

 inferior or ventral aspect of the thorax, and connected on 

 each side with the vertebral column by a series of more or 

 less ossified bars called ribs.^ 



It is present in all Mammals, but varies much in cha- 

 racter in the different groups. 



When in its usual and most complete form (see Fig. 31), 

 it may be divided into three parts, called respectively, — 



1. Presternuvi, or "manubrium sterni " of human ana- 

 tomy. 



2. Mesosterniijfi, body of the sternum or gladiolus. 



3. Xiphisteniuni^ xiphoid or ensiform process of the ster- 

 num. 



The mesosternum is usually composed of several distinct 

 segments, which may become ankylosed together, but more 

 often permanently retain their individuality, being con- 

 nected either by fibrous tissue or by synovial joints. 



^ For much valuable infoi-mation upon the structure and development 

 of the sternum, see W. K. Parker's " Monograph on the Shoulder-girdle 

 and Sternum of the Vertebrata," published by the Ray Society, 1868. 



