762 A MANUAL OF ANATOMY 



the more numerous. The white rami are composed of medullated 

 nerve-fibres, and are not more than three in number. They are 

 derived from the anterior primary divisions of the first three lumbar 

 nerves, and proceed to the ganglia. The grey rami pass from all 

 four ganglia to join the anterior primary divisions of the five lumbar 

 nerves. Both white and grey rami pass together beneath the 

 fibrous arches of the psoas magnus in company with the lumbar 

 vessels, and the communications with the lumbar nerves are estab- 

 lished close to the intervertebral foramina. The branches of 

 distribution proceed partly from the ganglia and partly from the 

 connecting cord, and are distributed to the coats of the aorta, the 

 bodies and ligaments of the lumbar vertebrae, and the hypogastric 

 plexus, the last branches crossing the common iliac artery. 



Receptaculum Chyli. — ^This is the dilated commencement of the 

 thoracic duct. Tt is situated deeply at the upper part of the 

 posterior abdominal wall in front of the bodies of the first and 

 second lumbar vertebrae, where it has the aorta on its left side and 

 slightly in front, and the right azygos vein on its right side. It is 

 overlapped by the right crus of the diaphragm. It is somewhat 

 elliptical, being about ^ inch broad at its widest part, and about 

 2 inches in length. Superiorly it becomes narrow, and is continued 

 into the thoracic duct, which enters the thorax through the aortic 

 opening of the diaphragm. It receives the following afferent 

 vessels from below upwards : the right and left lumbar lym- 

 phatic trunks from the median lumbar glands, which join its 

 lower narrow end ; some of the efferent vessels from the lateral 

 lumbar glands ; and the intestinal lymphatic trunk (or trunks) from 

 the mesenteric glands, which sometimes takes up the efferent vessels 

 of the coeliac glands, though these may enter the receptaculum 

 chyli independently. 



Azygos Veins. — ^These are three in number, namely, the vena 

 azygos major, or right azygos vein, the vena azygos minor or lower 

 left azygos vein, and the upper left, or accessory, azygos vein. 



The vena azygos major or right azygos vein usually commences in 

 the right ascending lumbar vein, which is formed by longitudinal 

 anastomosing branches passing between the lumbar veins in front 

 of the lumbar transverse processes, and so disposed as to form one 

 vein which communicates with the inferior vena cava and with one 

 or other of the following veins of the right side : the common iliac, 

 the internal iliac, the ilio-lumbar, or the lateral sacral. Sometimes, 

 however, the right azygos vein springs from the posterior aspect of 

 the inferior vena cava close to the right renal vein, or from that 

 renal vein itself, or from the first right lumbar vein. It ascends 

 upon the body of the first lumbar vertebra, where it lies on the 

 right side of the receptaculum chyli under cover of the right crus 

 of the diaphragm, and it enters the thorax through the aortic open- 

 ing of that muscle. For its subsequent course in the thorax, where 

 it terminates in the superior vena cava, sec the section of the thorax. 



The vena azygos minor or lower left azygos vein commences in 



