BACK ABDOMEN. 2fi5 



The kidney lies in front of the last two or three ribs, 

 and sometimes its lower extremity does not reach below 

 the twelfth rib. Its position is outside the erector spinae 

 muscle. 



The cauda equina commences at the second lumbar ver- 

 tebra. 



The descending colon may be opened without wounding 

 the peritoneum, in an operation called colotomy, by a trans- 

 verse incision, upon the left side, two fingers' breadth above 

 the crest of the ilium, outside the erector spinse muscle. 



The prominences of the posterior superior spinous pro- 

 cesses of the ilium should be noticed. Pressure during pro- 

 tracted confinement to the back in bed, frequently causes 

 the integument over them to slough, and gives rise to "bed- 

 sores." 



The gluteal artery emerges from the greater sacro-ischi- 

 atic foramen at a point which corresponds to the middle of 

 a line, drawn from the posterior superior spinous process 

 of the ilium to the upper border of the trochanter major. 



ABDOMEN. 



t The xiphoid cartilage of the sternum corresponds in 

 position to the tenth dorsal vertebra. Its variations in 

 shape and direction, in different subjects, should be ob- 

 served. 



The pulsations of the aorta may readily be felt, in an 

 emaciated person, through the abdominal parietes. It may 

 be compressed against the vertebral column. The bifur- 

 cation of the aorta corresponds to a point just below, and 

 a little to the left of, the umbilicus, and to the third lumbar 

 vertebra. 



The median line of the abdomen, which is sometimes 

 represented by a sulcus, corresponds to the linea alba. The 

 linese arcuatse, along the outer border of the recti mus- 

 cles, may be made apparent by throwing these into a state 

 of contraction. The trocar may be thrust through either 

 of these aponeurotic intervals in the operation of paracen- 

 tesis abdominis ; in the first named, just below the umbili- 

 cus ; in the second, at a point midway between the umbili- 

 cus and the anterior superior spinous process of the ilium. 



The epigastric artery pursues a course, indicated by a 

 line drawn from the middle of Poupart's ligament to a 

 point just above the umbilicus. 



The external abdominal ring may be explored, and pene- 

 23 



