THE BACK. 27 



measures about two and a half inches (6 cm.): the hilum, which looks mainly 

 forwards, is about two inches (5 cm.) from the median plane. 



Like other abdominal organs, the kidneys are subject to considerable variations 

 in size and position ; and they are frequently found at a lower level than that just 

 given. In the female they are situated as a rule slightly lower than in the male ; 

 and during childhood, when the kidneys are relatively of large size, they are at the 

 same time lower and more symmetrically placed than in the adult. 1 



The pancreas lies over the first and second lumbar vertebrae, from two and a 

 half to five inches (6 to 12 cm.) above the umbilicus ; and the third part of 

 the duodenum crosses the spine at a lower level, often reaching nearly to the 

 umbilicus. 



Abdominal vessels. The abdominal aorta commences rather above the mid- 

 point between the infrasternal depression and the umbilicus, and passes downwards 

 usually a little to the left of the middle line of the body, although its lower end 

 often occupies a median position, or may even extend over slightly to the right. 

 The bifurcation occurs on the average about three-quarters of an inch (2 cm.) below 

 the umbilicus, and the direction of the common and external iliac arteries is indicated 

 by drawing a line from this point to another midway between the pubic syrnphysis 

 and the anterior superior spine of the ilium. The inferior vena cava lies just to the 

 right of the aorta. 



The creliac axis arises opposite the lower part of the last dorsal vertebra, i.e., 

 between four and five inches (10 12 cm.) above the umbilicus ; the superior 

 mesenteric artery a very little lower ; the two renal arteries from three and a 

 half to four inches (9 10 cm.), and the inferior mesenteric about one inch 

 (2'5 cm.) above the umbilicus. 



THE BACK. 



At the back of the neck, a slight median depression the nuchal furroiv, com- 

 mencing immediately below the external occipital protuberance descends over the 

 ligamentum nuchae, between the prominences formed by the complexus and trapezius 

 muscles of the two sides. By pressing deeply in this furrow, the spine of the axis is 

 readily felt, and generally also the spines of the third, fourth, fifth, and sixth cervical 

 vertebras less distinctly. The furrow disappears gradually towards the root of the 

 neck, where the spines of the seventh cervical and upper one or two dorsal vertebras 

 become visible. The first spine to appear is usually that of the seventh cervical 

 vertebra, but sometimes the sixth is long and comes to the surface : the most 

 prominent is the first dorsal. They necessarily project more plainly when the neck 

 is inclined forwards. Below these, the long spinal or dorso-lumbar furroiv descends 

 in the middle line between the elevations formed by the erector spinae muscles 

 covered on each side above by the trapezius and below by the latissimus dorsi. The 

 furrow is deepest in the lower dorsal and upper lumbar regions, where the muscles 

 are thickest and most fleshy ; in the lower lumbar region and over the upper part of 

 the sacrum, the erector muscles are tendinous, and give rise to a somewhat lozenge- 

 shaped flattened area through which the groove is continued, becoming gradually 

 shallower, to terminate at the spine of the third piece of the sacrum (last sacral 

 spine) in the angle formed by the meeting of the right and left gluteus maximus 

 muscles. A little above and external to this point, a slight depression indicates the 

 position of the posterior superior iliac spine. At the bottom of the spinal furrow, 

 the spines may be felt and counted, the middle dorsal ones generally with consider 

 able difficulty in the erect position, but most of them are rendered very evident by 



1 See Second Annual Report of Committee of Collective Investigation of Anat. Soc., 1890-91, by 

 Arthur Thomson, Journ. Anat., xxvi, 83; also F. Helm, Beitriiye zur Kenntniss der Niercn-Topo- 

 graphie, Diss., Berlin, 1895. ' 



