936 THE VASCULAR SYSTEM. 



vertebrae, are the obturator nerve, the lumbo-sacral trunk, and the ilio-lumbar artery, which 

 form posterior relations to the common iliac artery of the corresponding side. 



Lateral. The lateral relations of each artery are coils of small intestine, and the 

 commencement of the inferior vena cava lies to the lateral side of the upper part of the 

 right artery. 



Medial. On the medial side of the right common iliac artery are the right common 

 iliac vein, below, and the left common iliac vein, above. The last-named vein lies on the 

 medial side of the left common iliac artery. 



Branches. The external iliac and the hypogastric are the only branches. 



ARTERIA HYPOGASTRICA. 



The hypogastric artery (O.T. internal iliac) (Figs. 773, 774, and 777) in the 

 foetus is the direct continuation of the common iliac trunk. It supplies numerous 

 branches to the pelvis, runs upwards on the anterior abdominal wall to the 

 umbilicus as the umbilical artery, and is prolonged through the umbilical cord 

 to the placenta. One of its pelvic branches the inferior glutaeal (O.T. sciatic) is 

 at first the main artery of the inferior extremity, but subsequently another branch 

 is given off which becomes the chief arterial trunk of the lower limb. This branch 

 is the external iliac artery ; it soon equals and ultimately exceeds the hypogastric 

 in size, and it is into these two vessels that the common iliac appears to bifurcate. 



When the placental circulation ceases and the umbilical cord is severed, the 

 umbilical part of the hypogastric trunk which extends from the pelvis minor to 

 the umbilicus atrophies, and is afterwards represented almost entirely by a fibrous 

 cord, known as the obliterated umbilical artery. It is only at its proximal end 

 that the atrophied part remains pervious, and there it forms the commencement 

 of the superior vesical artery. The permanent hypogastric is a comparatively 

 short vessel. Owing to the arrangement of some of its branches it appears to 

 end in an anterior and a posterior division, the former of which is to be regarded 

 as the continuation of the vessel, whilst the latter is simply a common stem oil 

 origin for some of the branches. 



With this explanation the artery may be described in the usual manner. 



It arises from the common iliac opposite the sacro-iliac articulation and at the 

 level of the lumbo-sacral articulation, and descends into the pelvis minor, tc| 

 terminate, as a rule, opposite the upper border of the greater sciatic notch, in fcwc 

 divisions anterior and posterior from each of which branches of distribution art 

 given off. The artery measures about 37 mm. (one and a half inches) in length. 



Relations. Anterior. Each hypogastric artery is covered antero-medially b} 

 peritoneum, behind which the corresponding ureter descends along the anterior borde] 

 of the artery. The pelvic colon crosses from the front to the medial side of the lefi 

 artery, and the terminal part of the ileum bears the same relation to the right artery. 



Posterior to it are the hypogastric vein and the commencement of the common iliai 

 vein ; still more posteriorly are the lumbo-sacral trunk and the sacro-iliac joint. 



Lateral. On its lateral side the external iliac vein separates it from the psoas majo 

 muscle, above. At a lower level the obturator nerve, embedded in a mass of fat, intervene: 

 between the hypogastric artery and the lateral wall of the pelvis. On its medial sid< 

 it is crossed by some of the tributaries of the hypogastric vein, and it is covered b; 

 peritoneum. 



Branches. The hypogastric artery supplies the greater part of the pelvi 

 wall and contents, and its branches are distributed also to the buttock and thig] 

 and to the external organs of generation. 



All the branches may be given off separately from a single undivided pareD 

 trunk, but as a rule they arise in two groups corresponding to the two divisions i 

 which the artery, under these circumstances, appears to end. 



fllio-lurnbar 

 Posterior division | parietal \ Lateral sacral 



[Superior gluteal 



