_g._ The eleventh and twelfth ribs can be felt even in corpulent persons, outside the erector spinæ, sloping downwards. _h._ One should remember the fact that the sternal end of each rib lies on a lower level than its corresponding vertebra. For instance, a line drawn horizontally backwards from the middle of the third costal cartilage at its junction with the sternum, to the spine, would touch the body, not of the third dorsal vertebra, but of the sixth. Again, the end of the sternum would be on about the level of the tenth dorsal vertebra. Much latitude must be allowed here for variation in the length of the sternum, especially in women. 39. =Interval below clavicle.=--Immediately below the clavicle we recognise the triangular interval between the pectoralis major and the deltoid. This space varies in different cases, depending on the distance between the muscles. It is important as a guide to the coracoid process and the axillary artery. In a case of injury to the shoulder, to ascertain whether the coracoid process is broken, carry the arm outwards, to put the deltoid and pectoral muscles on the stretch, and make manifest the space between their opposite borders. Pressing the thumb into the space we can feel the inner side of the coracoid process, the apex being under the fibres of the deltoid; thus it is easy to ascertain whether it be broken. Moreover, this space corresponds with the line of the axillary artery; here its pulsation can be distinctly felt, and here it can be compressed (but not easily, or for long) against the second rib. 40. =Internal mammary artery.=--The line of the internal mammary artery runs perpendicularly behind the cartilages of the ribs, about half an inch from the sternum. The perforating branch through the second intercostal space is generally the largest. 41. =Outline of heart on chest-wall.=--To have a general idea of the form and position of the heart, map its outline on the wall of the chest, as follows:-- _a._ To define the base draw a transverse line across the sternum corresponding with the upper borders of the third costal cartilages: continue the line half an inch to the right of the sternum and one inch to the left. _b._ To find the apex, mark a point about two inches below the left nipple, and one inch to its sternal side. This point will be between the fifth and sixth ribs. _c._ To find the lower border (which lies on the central tendon of the diaphragm), draw a line, slightly curved downwards, from the apex across the bottom of the sternum (not the ensiform cartilage) as far as its right edge. _d._ To define the right border (formed by the right auricle), continue the last line upwards with an outward curve, so as to join the right end of the base. _e._ To define the left border (formed by the left ventricle), draw a line curving to the left, but not including the nipple, from the left end of the base to the apex.