436 AETERIES OF THE ABDOMEN. 



arise in. the mode ordinarily described ; viz., as two separate vessels from the 

 abdominal aorta. (Op. cit. p. 417.) 



Lumbar arteries.- — Tlie Inmhar arteries resemble the intercostal 

 arteries, not only in their mode of orij^in, bnt also in a creat measure 

 in the manner of their distribution. They arise from the back part 

 of the aorta, and are usually four in number on each side. They 

 pass outwards, each resting on the body of the corresponding lumbar 

 vertebra, from the first to the fourth, and soon dip deeply under the 

 psoas muscle. The two upper arteries are likewise under the pillars of 

 the diaphragm ; and those on the right side are covered by the vena 

 cava. At the interval between the transverse processes, each lumbar 

 artery divides into an aMominal and a dorsal branch. 



Branches. — (c?) The nhrhn/ii/i/jl branch of each lumbar arteiy runs outwards 

 behind the quadi-atus lumborum, — the lowest of these branches not unfrequently 

 in front of that muscle. Continuing- outwards between the abdominal muscles, 

 the artery ramifies in their substance, and maintains communications with 

 branches of the epigastric and internal mammary in front, with the tenninal 

 branches of the intercostals above, and with those of the ilio-lumbar and circum- 

 flex iliac arteries below. 



(h) The dovfial branch of each lumbar artery, like the coiTesponding branch of 

 the intercostal arteries, gives off, immediately after its origin, an offset, named 

 .\pinal, which enters the spinal canal. The dorsal branch then proceeding back- 

 wards with the jDOsterior primary branch of the corresponding lumbar nerve 

 between the transverse processes of the vertebra?, divides into smaller vessels, 

 which are distributed to the muscles and integuments of the back. 



{c) The sjjinal branch enters the spinal canal through the intervertebral fora- 

 men, and. having given an offset ■v^■hich rims along the nerves to the dm-a mater 

 and Cauda equina, it communicates with the other spinal arteries, and divides 

 into two branches, which are distributed to the bones in the following manner :— 

 one cui-ves upwards on the back part of the body of the vertebra above, near to 

 the root of the pedicle, whilst the other descends in a similar manner on the 

 vertebra below ; and each communicates with a coiTesponding branch from the 

 neighbouring spinal artery. As this arrangement prevails on both sides and 

 throughout the whole length of the spine, there is fonned a double series of 

 arterial arches behind the bodies of the vertebrte, the convexities of which are 

 turned towards each other. From the arches on opposite sides offsets are dhected 

 inwards at intervals to reinforce a median longitudinal vessel, which extends 

 along the spine like the single arteiy on the front of the spinal cord. The arches 

 are moreover joined together across the bodies of the vertebne by transverse 

 branches. 



From this interlacement of vessels, numerous ramifications are distributed to 

 the periosteum and the bones. 



Varieties. — The himhiif ai-teriesof opposite sides, instead of taking their origin 

 separately from the aorta, occasionally commence by a common tmnk, whose 

 branches pass out laterally, and continue their course in the ordinary way. Two 

 arteries of the same side are sometimes conjoined at their origin. On the last 

 lumbar vertebra, the place of a lumbar artery is often taken by a branch from 

 the middle sacral artery, and the ilio-lumbar compensates for the absence of the 

 lumbar vessel amongst the muscles. 



MIXUTE ANASTOilOSES OF THE VISCEKAL AND PAKIETAL BKAJS'CEES OF . 

 THE ABDOMINAL AOKTA. 



The existence of minute anastomoses between some of the visceral branches of 

 the abdominal aorta and those supplying the wall of the cavity has been recog- 

 nised by several anatomists, and various examples have been noticed in the pre- 

 vious description. These communications have been more distinctly proved and. 



