The pelvis is divided into true and false. The false pelvis is. the abdomen proper, the part that is enclosed in front only by muscle and fascia. The true pelvis, or pelvic cavity, is the part which is bounded in front by the pubes, the upper surface of which is the brim. The ridge is called the ilio-pectineal line. The abdomen proper is in a nearly straight line from the thorax. The pelvic cavity goes very distinctly backwards.

Fig. 76.—Nine Divisions of the Abdomen. Approximate Position of the Organs.

The abdomen is further divided into nine regions by four imaginary lines, two horizontal and two vertical. The horizontal are supposed to pass (1) from the lowest part of the tenth costal arch on one side to the corresponding spot on the opposite side ; (2) from the highest point of one iliac crest to the other. The vertical are parallel with the middle line of the body, from a point midway between the symphysis pubes and the highest point of the ilium, passing upwards to the breasts.

In the upper region there are three divisions :

Right and left hypochondriac. Epigastric in the middle.

In the middle region there are three divisions :

Bight and left lumbar. Umbilical in the middle.

In the lower region there are three divisions :

Eight and left iliac. Hypogastric in the middle.

The upper region is called the costal zone. The middle region is the umbilical zone. The lower region is the hypogastric zone.

The contents of the abdomen are the stomach, small and large intestines, liver, with gall-bladder, pancreas, spleen, two kidneys, two suprarenal capsules, two ureters, bladder, receptaculum chyli, abdominal aorta with its branches, inferior vena cava with its tributaries, plexuses of nerves (spinal and sympathetic), and lymphatic glands and vessels.

Fig. 77.—Viscera of the Thorax and Abdomen.

1. Lungs ; 2, heart ; 3, left lobe of liver, turned back ; 4, right lobe of liver, turned back ; 5, stomach ; 6, spleen ; 7, transverse colon ; 8, ascending colon; 9, descending colon ; 10, sigmoid flexure ; 11, rectum; 12, bladder.