DISSECTION OF THE ABDOMEN. 331 



limb, pelvis, and spermatic cord ; and the efferent vessels from the most 

 anterior group (lumbar) pass to enter the receptaculum chyli. 



The Posterior Aorta (Plates 44 and 45). The abdominal portion of 

 this great artery appears close to the spine, between the two pillars of 

 the diaphragm, the opening being termed the hiatus aorticus. It passes 

 backwards across the lumbar vertebral bodies, resting on the left pillar 

 of the diaphragm and the inferior common ligament. At the 5th 

 lumbar vertebra it terminates in four branches, two diverging to each 

 side. These are the external and internal iliac arteries. On its right 

 side the aorta is related to the vena cava. On the left it is related to 

 the psoas parvus, the left lumbar sympathetic cord, and the left kidney 

 and suprarenal capsule ; and the left ureter is beside or in actual 

 contact with it. Besides the external and iliac arteries, which are 

 described as its terminal branches, it gives off the following : — 



1. Phrenic Branches (two or three) to the pillars of the diaphragm. 

 They are given off at the hiatus aorticus. 



2. Lumbar Arteries. There are six or seven of these on each side. 

 The last comes from the lateral sacral artery, the second last from the 

 internal iliac, and the others from the aorta. These last arise from the 

 upper aspect of the vessel, and divide into two branches — a superior for 

 the skin and muscles over the lumbar vertebrae, giving also a spinal 

 twig through the intervertebral foramen ; and an inferior which passes 

 outwards in the intertransverse spaces to the flank, where it anasto- 

 moses with the circumflex iliac artery in supplying the abdominal 

 muscles. 



3. The Middle Sacral Artery is an extremely slender vessel, and not 

 always present. Search for it in the angle between the internal iliacs. 

 Arising from the summit of that angle, it passes mesially backwards on 

 the sacrum. It is of interest as representing the large vessel which in 

 some animals continues the aorta to the coccygeal region. 



4. The Coeliac Axis is detached as soon as the aorta passes through 

 the hiatus aorticus. 



5. The Anterior Mesenteric — the largest of the branches — is detached 

 at the 1st lumbar vertebra. 



6. The Renal Arteries, right and left, arise from the sides of the 

 aorta at the articulation between the 1st and 2nd lumbar vertebrae. 



7. The Spermatic Arteries, right and left, come off a few inches 

 behind the renals, viz., between the 3rd and 4th lumbar vertebrae, and 

 one generally a little in advance of the other. As seen in the dissection, 

 each passes obliquely backwards and outwards over the ureter and 

 circumflex iliac artery to gain the internal abdominal ring, where it 

 joins the other constituents of the spermatic cord. In the cord it has 

 a remarkably tortuous disposition ; and, although a long vessel, it 

 detaches no branches of any size until it reaches the testicle. In the 



