DISSECTION OF THE ABDOMEN. 321 



of the sympathetic nerve ; and, lastly, a group of muscles, comprising 

 the iliacus, psoas magnus, psoas parvus, quadratus lumborum, and 

 lumbar intertransverse muscles. The great arterial and venous trunks 

 are mesially placed, and the aortic plexus is on the great artery. The 

 other structures enumerated are the same on both sides of the body. 

 One side may be used for the nerves and the arterial and venous 

 branches, the other being reserved for the muscles. In the mare, after 

 the ovarian and uterine vessels have been examined, the broad ligaments 

 must be cut to allow of the ovaries and uterus being pushed into the 

 pelvic cavity, where they are to remain until they can be dissected along 

 with the other reproductive organs of the female. 



Lymphatic Glands. In cleaning the nerves and vessels, the follow- 

 ing groups of lymphatic glands will be found : — 1. Sacral glands, 

 between the right and left internal iliac arteries at the entrance to the 

 pelvis. 2. Internal Iliac glands, between and around the roots of the 

 external and internal iliac arteries on each side. 3. External Iliac 

 glands towards the point of bifurcation of the circumflex iliac artery. 

 4. Lumbar glands, on the lower face of the aorta around the roots of the 

 posterior mesenteric and spermatic arteries. These various groups of 

 glands are placed on the course of the lymphatic vessels of the hind 

 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 back- 

 wards 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 Brcmches (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 out- 

 wards in the intertransverse spaces to the flank, where it anastomoses 

 with the circumflex iliac ai'tery in supplying the abdominal muscles. 



Y 



