MUSCLES OF THE TRUNK AND CHEST. 213 



External, into the anterior border of each succeeding rib. 

 Internal, into the posterior border of each rib before. ^ 



Sterno cost ales. Origin. From the hgament in the 

 centre of the superior surface of the sternum. Insertion. 

 Into the bone and cartilage of the second to the seventh 

 ribs. The muscles are within the chest, and covered by 

 the pleurse. 



All these muscles are so blended that it is unsatisfactory 

 to speak of them separately, therefore we prefer to allude 

 to their actions in another place. 



First, to speak about the diaphragm and intercostals, 

 which are more especially muscles of respiration, and to 

 which all the others are accessories, used on particular 

 occasions ; though some, as the longissimus dorsi, are only 

 used in cases of extreme distress. 



The diaphragm or 77iidriff {see Fig 21), is a most im- 

 portant muscle, and, like the heart, is, during life, in con-^ 

 stant action. It is a broad, thin, and tendinous expansion 

 in the middle, having fleshy or muscular sides ; it is so 

 situated as to form a complete division between the thorax 

 and abdomen; its upper part, opposed to the back, ex- 

 tends posteriorly till its crurae are under the loins, and 

 even reach the sacrum ; while the anterior part is attached 

 to the hindmost part of the sternum. In a state of rest, it 

 is anteriorly convex, and posteriorly concave ; the surface 

 opposed to the thorax being covered by the pleurse, and 

 that towards the abdomen by the peritoneum. From some 

 pecuharities in the disposition of its fibres, it is sometimes 

 described as two muscles ; the great and little diaphragm. 

 The anterior or larger portion arises by distinct fleshy fibres 

 from the ensiform cartilage of the sternum ; from the in- 

 ternal surface of the cartilages of the eighth, and all the 

 remaining ribs, excepting the last two. From these ori- 

 gins, the fibres are directed like radii from the circum- 

 ference {Fig 21 . 2, 2, 2) to the tendinous centre of a cir- 

 cle ; which is perforated by a hole, a Uttle inclined to the 

 right side, called the foramen dextrum {Fig2\ . 7), and 

 furnishing a passage for the vena cava. — The lesser portion 

 of the diaphragm fills up the space close to the spine {Fig 

 21 . 3, 4) ; arising by two different portions from the six- 

 teenth dorsal, and from all the lumbar vertebrae, and are called 



