48. =Median furrow.=--In a muscular man, a furrow, caused by the prominence of the erector spinæ on each side, runs down the middle of the back. The lower end of the furrow corresponds with the interval between the spine of the last lumbar and that of the first sacral vertebra. 49. =Spines of vertebræ.=--A little friction with the fingers down the backbone will cause the spines of the vertebræ to be tipped with red, so that they can be easily counted, and any deviation from the straight line detected. Still it is worth remembering that the spine of the third dorsal is on a level with the commencement of the spine of the scapula--that the spine of the seventh dorsal is on a level with the inferior angle of the scapula--that the spine of the last dorsal is on a level with the head of the last rib. =Division of the trachea.=--The division of the trachea is opposite the spine of the third, in some cases the fourth, dorsal vertebra. In front this division is on the level of the junction of the first with the second bone of the sternum. The root of the spine of the scapula is marked by a slight dimple in the skin. This is on a level with the third intercostal space. A stethoscope placed on the inner side of this dimple would cover the bronchus, more especially the right, since it is nearer to the chest wall. Make a man lean forwards, with his arms folded across the chest; this will make prominent the spines of the vertebræ. The lower border of the trapezius will guide you to the spine of the twelfth dorsal vertebra. 50. The place where the kidney is most accessible to pressure is below the last rib, on the outer edge of the erector spinæ. 51. The highest part of the ilium is about the level of the fourth lumbar spine. The best incision for opening the descending colon is in a slightly sloping line beginning at the outer edge of the erector spinæ, midway between the crest of the ilium and the last rib, and continued across the flank for three inches or more, according to the amount of subcutaneous fat. 52. In the pit of the neck we can feel the trapezius and the ligamentum nuchæ. By pressing deeply we detect the forked and prominent spine of the second cervical vertebra. 53. The spines of the third, fourth, and fifth cervical vertebræ recede from the surface to permit free extension of the neck, and cannot often be felt. But the spines of the sixth and seventh (v. prominens) stand out well. 54. Notice that most of the spines of the dorsal vertebræ, owing to their obliquity, do not tally with the heads of their corresponding ribs. Thus, the spine of the second dorsal corresponds with the head of the third rib; the spine of the third dorsal with the head of the fourth rib, and so on till we come to the eleventh and twelfth dorsal vertebræ, which do tally with their corresponding ribs. All this, however, is best seen in the skeleton.