SPINAL AND SYMPATHETIC NERVES. 495 



Lymphatic glands. A chain of glands is placed along the side of the 

 external iliac artery, and along the front and sides of the lumbar vertebras ; 

 they are connected by short tubes, which increase in size and diminish in 

 number, until at the upper part of the lumbar vertebrae three or four 

 trunks unite in the thoracic duct. Into the glands the lymphatics of 

 the lower limbs, and those of the viscera and wall of the abdomen are 

 received. 



Receptaculum chyli (Pecquet). The thoracic duct begins in the ab- 

 domen by the union of three or four large lymphatic vessels. Its com- 

 mencement is marked by a dilatation, which is placed on the right side of 

 the aorta, about opposite the first lumbar vertebra. The duct enters the 

 thorax by passing through the diaphragm with the aorta. 



Beginning of the azygos veins. The right vein (vena azygos major) 

 begins opposite the first or second lumbar vertebra by a small branch, 

 which is united with a lumbar vein. It enters the thorax with the tho- 

 racic duct and the aorta, to the right of which it lies. 



The left or small azygos vein begins on the left side of the spine, joining 

 one of the lumbar veins, and passes through the pillar of the diaphragm, 

 or through the aortic opening. 



The anatomy of these veins is given in the description of the thorax, 

 p. 338. 



SECTION VI. 



SPINAL AND SYMPATHETIC NERVES. 



THE spinal nerves of the loins are united in a plexus, and supply the 

 limb and the contiguous parts of the trunk. 



Dissection. The lumbar nerves and their plexus are to be learnt on the 

 left side, although the woodcut shows them on the right side ; and to bring 

 them into view, the dissector should cut through the external iliac vessels, 

 and afterwards scrape away the psoas. For the most part the fleshy fibres 

 may be removed freely ; but a small branch (accessory of the obturator) 

 should be first looked for at the inner border of the muscle. In the sub- 

 stance of the quadratus lumborum a communication may be sometimes 

 found between the last dorsal and the first lumbar nerve. 



The cord of the sympathetic nerve lies along the edge of the psoas, and 

 offsets of it join the spinal nerves ; these are to be followed back along the 

 lumbar arteries. 



On the right side the psoas is to be left untouched, in order that the 

 place of emergence of the different nerve branches from it may be noticed. 



LUMBAR SPINAL NERVES. The anterior primary branches of the lum- 

 bar nerves enter the lumbar plexus, with the exception of the last. Five 

 in number, they increase in size from the first to the last, and are joined 

 by filaments of the sympathetic near the intervertebral foramina. Before 

 entering the plexus they supply branches to the psoas and quadratus lum- 

 borum muscles. 



The fifth nerve (fig. 177) receives a communicating branch from the 

 fourth, and is to be followed into the pelvis to its junction with the sacral 

 plexus. After the two are united, the name lumbo-sacral is applied to 



