LUMBAR ARTERIES. 417 



In only one out of thirty-six cases observed by R. Quain did the phrenic arteries 

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

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



II. LUMBAR ARTERIES. 



The lumbar arteries resemble the intercostal arteries, not only in their 

 mode of origin, but also in a great measure in the manner of their distribu- 

 tion. They arise from the back part of the aorta, and are usually four in 

 number on each side. Taey 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 a dorsal and an abdominal branch. 



BRANCHES. (a) The abdominal branch of each lumbar artery runs outwards 

 behind the quadratus 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 terminal branches of the inter- 

 costals above, and with those of the ilio-lumbar and circumflex iliac arteries below. 



(b) The dorsal branch of each lumbar artery, like the corresponding branch of the 

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

 which enters the spinal canal. The dorsal branch then, proceeding backwards with 

 the posterior primary branch of the corresponding lumbar nerve between the trans- 

 verse processes of the vertebrae, divides into smaller vessels, which are distributed to 

 the muscles and integuments of the back. 



(c) The spinal branch enters the spinal canal through the intervertebral foramen, 

 and, having given an offset which runs along the nerves to the dura 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 curves 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 com- 

 municates with a corresponding branch from the neighbouring spinal artery. As 

 this arrangement prevails on both sides and throughout the whole length of the spine, 

 there is formed a double series of arterial arches behind the bodies of the vertebrae, 

 the convexities of which are turned towards each other. From the arches on opposite 

 sides offsets are directed inwards at intervals to reinforce a median longitudinal 

 vessel, which extends along the spine like the single artery on the front of the spinal 

 cord. The arches are moreover joined together across the bodies of the vertebrae by 

 transverse branches. 



From this interlacement of vessels, numerous ramifications are distributed to the 

 periosteum and the bones. 



PECULIARITIKS. The lumbar arteries of opposite sides, instead of taking their 

 origin separately from the aorta, occasionally commence by a common trunk, 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. 



MINUTE ANASTOMOSES OF THE VISCERAL AND PARIETAL BRANCHES OF 

 THE ABDOMINAL AORTA. 



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

 abdominal aorta and those supplying the walls of the cavity has been recognised by 

 several anatomists, and various examples have been noticed in the previous descrip- 

 tion. These communications have recently been more distinctly proved and their 

 nature elucidated by W. Turner in a series of experimental injections, made with a 

 view to their detection. (" Brit, and For. Med. Chirug. Review," July, 1863.) 



