THE THORAX. 



181 



the middle of the clavicle it is so deep from the surface as not to be accessible and 

 here the second rib is the one which shows just below the clavicle. In children the 

 point of junction of the cartilages and ribs can often be distinguished; this is par- 

 ticularly so in cases of rachitis. 



The line of junction between the body of the sternum and the ensiform cartilage 

 can be distinguished, and to each side of it is felt the cartilage of the seventh rib, 

 the last that articulates with the sternum. The tenth rib is the lowest which is 

 attached anteriorly, the eleventh and twelfth being shorter and floating ribs. The 

 intercostal spaces are wider anteriorly than posteriorly and the third is the widest. 



The nipple is usually in the fourth interspace or on the lower border of the fourth 

 rib and on a Iin6 a little to the outer side of the middle of the clavicle. In women its 

 position is variable, owing to the breasts being pendulous. The mammary gland 

 reaches from the third to the seventh rib. As the pectoralis major muscle does not 

 arise lower than the sixth rib it is seen that the mammary gland projects beyond it, an 

 important fact to be remembered in operations for removal of the breast. 



Immediately to the outer side of the upper edge of the pectoralis major, beginning 

 at the middle of the clavicle and below it, is a hollow. This is the interval between 

 the pectoralis major and deltoid muscles. At its upper end it is equal in width to one- 



Suprasternal notch 

 Sternal end of first rib \ 

 Second rib 



Sp 



ace between deltoid and pectoralis major 

 Outer end of clavicle 

 Coracoid process 



Acromioclavicular joint 

 Acromion process 



Angle of sternum 

 opposite second rib 



Xiphosternal 

 articulation 



Serrations of serratus 

 anterior muscle 



Tip of ensiform process 

 Infrasternal depression 



FIG. 204. Surface anatomy of the thorax. 



sixth the length of the clavicle, because the deltoid is attached only to the outer 

 third of the clavicle. Immediately beneath the edge of the deltoid muscle and about 

 2.5 cm. below the clavicle is the coracoid process. On abducting the arm the scapula 

 is rotated and the serratus anterior muscle is put on the stretch; this makes its four 

 lower serrations visible. The serration attached to the fifth rib is the highest, the 

 sixth is the most prominent and extends farthest forward, while below are the last 

 two attached to the seventh and eighth ribs. The operation of paracentesis, or tapping 

 for pleural effusion, is most often done in the sixth interspace in the midaxillary line. 

 This will be about on a level with the nipple. The apex beat of the heart is felt in 

 the fifth interspace, about 2. 5 cm. ( i in. ) to the inner side of the line of the nipple. 



Running down behind the costal cartilages and crossing the intercostal spaces 

 about a centimetre from the edge of the sternum is the internal mammary artery. 

 When it reaches the sixth interspace it divides into the superior epigastric, which 

 goes downward in the abdominal walls, and the musculophrenic, which passes to the 

 attachment of the diaphragm along the edge of the chest. 



( The relations of the organs of the chest to the surface will be discussed later. 

 The nervous supply to the surface of the chest is of interest mainly as indicating the 

 probable location of the lesion in cases of fracture of the spine, and it will be described 

 in the section devoted to the Back.) 



