THE BUTTOCKS.
103.Buttocks.—Bony landmarks.—The bony landmarks of the buttocks which can be distinctly felt are: 1, the posterior superior spines of the ilia; 2, the spines of the sacral vertebræ; 3, the two tubercles of the last sacral vertebra; 4, the apex of the coccyx in the deep groove leading to the anus; 5, the tuberosities of the ischia on each side of the anus.
The posterior spines of the ilia are about the level of the second sacral spine, and correspond with the middle of the sacro-iliac symphysis.
The third sacral spine marks the lowest level to which the membranes of the cord and the cerebro-spinal fluid descend in the spinal canal.
The tuberosities of the ischia, in the erect position, are covered by the gluteus maximus. In the sitting position they support the weight of the body, and are only covered by a thick pad of coarse fat. Between this pad and the bones there is a bursa, which becomes occasionally enlarged and inflamed in coachmen.
The prominence of the nates is one of the characteristics of man in connection with his erect attitude. ‘Les fesses n’appartiennent qu’à l’espèce humaine.’ They are formed of an accumulation of fat over the great muscle of the buttock (gluteus maximus). From their appearance we may gather some indication of the state of the constitution. They are firm and globose in the vigorous; loose and flaccid in the infirm. Wasting and flattening of one, compared with the other, is an early symptom of disease in the hip.
104.Fold of the buttock.—The deep furrow, termed‘the fold of the buttock,’ which separates the nates from the back of the thigh, corresponds with the lower border of the gluteus maximus. Its altered direction in disease of the hip is very characteristic. This is the best place to feel for the great ischiatic nerve. We find it by pressing deeply between the trochanter and the tuber ischii, rather nearer to the latter. When we sit upright, the nerve is not liable to pressure; but it becomes numbed when we sit long sideways.
105.Gluteal artery.—To find at what point the gluteal artery comes out of the pelvis, draw a line from the posterior superior spine of the ilium to the top of the trochanter major, rotated inwards. The junction of the inner with the middle third of this line lies over the artery as it emerges from the upper border of the great ischiatic notch.
The point of exit of the ischiatic artery from the pelvis is about half an inch lower than that of the gluteal.
106.Pudic artery.—The pudic artery crosses the spine of the ischium. To find it, draw a line from the outer side of the tuber ischii to the posterior superior spine of the ilium. The junction of the lower with the middle third gives the position of the artery. The ischiatic artery lies close to it, but nearer the middle line.
Looking at the course of these arteries it appears that when we sit on hard seats the pressure is sustained by the bones; when we recline on soft seats the pressure is sustained more by the soft parts, and reaches the arteries; hence the tendency of modern modes of reposing to drive the blood into the interior of the pelvis and favour the production of piles and uterine disorders. A celebrated French accoucheur used to say that the fashion of high waists, tight lacing, and easy chairs brought him many thousands a year.