This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
On looking at the chest one should note whether or not it appears normal. It may show the rounded form of emphysema or the flat form of phthisis. One side may be larger than the other, suggesting pleural effusion. The intercostal spaces may be obliterated, indicating the same condition. This may be local instead of over the whole chest. Note whether Harrison's groove, funnel and pigeon breast, or beading of the ribs, already described, are present. Aneurism affecting the great vessels may cause a bulging in the upper anterior portion, and cardiac disease may produce marked changes in the apex beat. This may be displaced to the right side by pleural effusion.
The clavicle belongs to the shoulder-girdle and hence will be described with the upper extremity. Both it and the sternum are subcutaneous and can readily be felt beneath the skin. The point of junction of the first and second pieces of the sternum is opposite the second costal cartilage. It forms a distinct prominence, which is readily felt and is a most valuable landmark. It is called the angulus sterni or angle of Ludwig. There is usually a palpable depression at the junction of the second piece of the sternum and xiphoid cartilage.
The tip of the xiphoid or ensiform cartilage can be felt about 4 cm. below the joint between it and the second piece of the sternum. The top of the sternum is opposite the lower edge of the second thoracic vertebra. The angulus sterni is opposite the fifth vertebra, the lower end of the second piece of the sternum is opposite the tenth, and the tip of the ensiform cartilage is opposite the eleventh thoracic vertebra. There is usually comparatively little fat over the sternum, so that in fat and muscular people its level is below that of the chest on each side. Above its upper end is the suprasternal notch or depression, below its lower end is the infrasternal depression or epigastric fossa, sometimes called the scrobiculus cordis.
With the upper end of the sternum articulate the clavicles. The sternoclavicular joint possesses an interarticular cartilage between the clavicle and the sternum. This separates them sufficiently to allow the formation of a distinct depression, which can readily be felt. From the sternum to the acromion process the clavicle is subcutaneous. Below the inner end of the clavicle the first rib can be often seen and felt. At 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 particularly 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 line 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 onesixth 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. (1 in.) to the inner side of the line of the nipple.
Fig. 204. - Surface anatomy of the thorax.
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).