290 ZOOTOMY. 



128. The sternum, a bony bar in the middle line of the 

 chest, ending behind in a large discoidal cartilage, the 

 xiphoid process. 



129. The small, incompletely ossified clavicles, pass- 

 ing each from the upper extremity of the sternum to the 

 corresponding shoulder. 



130. The sterno-mastoid, a long slender muscle, 

 arising in conjunction with its fellow of the opposite side 

 from the anterior end of the sternum, and passing obliquely 

 forwards and outwards to the skull, just internal to the ex- 

 ternal jugular vein. 



131. The pectoralis major, a large muscle, covering 

 the ventral wall of the thorax : its fibres pass from the side 

 of the sternum upwards and outwards to the upper arm. 



The fibresof the pectoralis major pass either directly outwards, or, in 

 the posterior part of the muscle, outwards and forwards, and are 

 gathered into a strong bundle which is inserted into the deltoid ridge of 

 the humerus. 



132. The pectoralis tenuis, a thin sheet of transverse fibres cover- 

 ing the anterior part of the pectoralis major. 



133. The pectoralis minor, seen by removing the pectoralis major 

 and tenuis : it is a triangular muscle arising from the sternum, and 

 inserted partly into the clavicle, partly into the scapula (see 401). 



134. The ribs, largely concealed by the pectoral 

 muscles ; each consists of a bony portion (vertebral rib) 

 attached to the vertebral column, and of a cartilaginous 

 portion (sternal rib), attached to the sternum : they are 

 best seen by removal of the pectoral muscles. 



135. The external intercostal muscles, short fibres 

 filling up the interspaces between successive ribs : they are 

 very transparent in the fresh subject, allowing the pink 

 lungs to be seen through them. 



136. The blood-vessels and nerves of the arm, 



