536 



HUMAN ANATOMY. 



separated on the same line. No effort has been made, therefore, to show the latter 

 muscle in the diagram. 



Incisions Nos. i, 2, and 3 are through the linea alba, No. 2 being carried 

 around the umbilicus to the left to avoid the parumbilical vein and the round liga- 

 ment of the liver. The chief advantage is the accessibility to the whole cavity 

 afforded by prolonging the incision. The slight vascularity of the median raphe 

 and the thinness of the abdominal wall, while operative advantages, tend to favor 

 the later production of hernia. 



Incision No. 4 combines the disadvantages of the incisions through the linea 

 alba with the added interference with the nerve-supply to the rectus. 



Incision No. 5 (McBurney) is described later (page 1685). It represents 

 merely the separation of the aponeurotic fibres of the external oblique ; the deeper 

 wound separates the internal oblique and transversalis fibres transversely. It may 

 be noted that its inward extension (Weir), even if it involves division instead of 



retraction of the rectus (page 1685), 

 Fig. 536. would equally avoid nerve-trunks, but 



might involve ligation of the deep epi- 

 gastric. The resulting scar in the 

 rectus would, however, merely add in 

 effect another linea transversa and 

 would not impair the efficiency of that 

 muscle. 



Incision No. 6 (Eads) separates 

 the same structures, but affords a bet- 

 ter opportunity for approach to many 

 appendicular abscesses without going 

 through the peritoneal cavity (page 

 1685). 



The incision for inguinal colos- 

 tomy (page 1688) may be made on the 

 same lines as those just described. 



Incision No. 7, after division of 

 the external oblique, permits the sepa- 

 ration of the fibres of the internal ob- 

 lique and of the upper abdominal in- 

 tercostal nerves, which, like the others, 

 run beneath that muscle, and is used 

 to gain access to the gall-bladder 

 region. 



Incision No. 8 also respects the 

 internal oblique fibres and the seventh and eighth intercostal nerves and, when 

 used for gastrostomy, permits the development of a valvular or sphincteric action 

 about the orifice (page 1633). 



Incision No. 9 — the vertical incision through the rectus recommended for gas- 

 trostomy (Howse) — must divide the terminal branches of the intercostal nerves, and 

 consequently that portion of the muscle distal to the line of division will be weakened 

 or paralyzed and unable to contribute to the formation of a sphincter (Eads). 



The incision for lumbar colostomy is described later (page 1688). The re- 

 maining incisions through the loin may be more appropriately considered in relation 

 to the approach to the kidneys or ureters (page 1894). 



Anatomical Relations bearing on the Exaynitiation of the Abdomen. — Harris has 

 suggested utilizing the fixed and circuitous route of the colon (Fig. 1383) to subdi- 

 vide the abdominal cavity by taking the inner or mesial layers of the longitudinal 

 mesocolons and the inferior layer of the transverse mesocolon as the dividing lines. 

 We would thus obtain four regions, — namely, (i) the central region surrounded by 

 mesocolon, (2) the superior region lying above the transverse mesocolon, (3) the 

 right postero-lateral and (4) the left postero-lateral regions lying external to and 

 behind the longitudinal mesocolons. 



Tumors of special viscera begin, as a rule, in the region normally occupied by 



Diagram illustrating relations of various incisions to 

 structures of abdominal walls. 



