The inferior left colic goes to the sigmoid flexure of the colon, and soon divides into two branches; one superior anastomoses by an arch with the descending branch of the preceding, and the other inferior meets a branch of the hemorrhoidal in the meso-rectum. They are distributed to the intestine in a similar manner with the branches of the right colic arteries, as already described.
When the inferior mesenteric has given off the colic arteries, it diminishes, takes a perpen dicular direction, and reaches the posteror sur face of the rectum lodged between the layers of the meso-rectum, here it takes the name of superior hemorrhoidal artery. It soon divides into two branches, a right and left, which apply them selves to the sides of the rectum, sending branches backwards and forwards round that intestine, by which they communicate with each other, and anastomose below with the middle and inferior hemorrhoidal arteries ; some branches anastomose with the lateral sacral of the internal iliac.
The lateral branches of the abdominal aorta consist of the capsular, renal or emulgent, spermatic arteries, small twigs to the ureters and adipose substance in the vicinity of the aorta, and the four pairs of lumbar arteries. For an account of the capsular, emulgent, and sper matic arteries we must refer to the articles RENAL CAPSULE, KIDNEY, and TESTICLE.
The lumbar arteries are four in number on each side (fig. 78,f); they arise from the lateral and posterior part of the aorta nearly at right angles, they pass outwards across the middle of the bodies of the four superior lumbar or abdo minal vertebra to the roots of their transverse processes, covered by the psoas muscle and the crura of the diaphragm. When the lumbar arteries have reached the roots of the transverse processes of the lumbar vertebra, they divide each into two branches, one posterior and the other anterior.
The posterior or dorsal branches are smaller and pass backwards between the transverse processes of the lumbar vertebra, opposite the intervertebral foramina, where they each send a branch inwards to the spinal cord and cauda equina; they then plunge into the substance of the great sacro-lumbar mass of muscles, in which they are lost, anastomosing frequently with each other, and with the dorsal branches of the low est intercostal and ileo-lumbar arteries. The continuations or anterior divisions of the lum bar arteries pass outwards between the psoas and quadratus lumborum muscles, to which they give small branches, as well as to the diaphragm, kidney, renal capsule, and surrounding cellular membrane ; they then continue their course forwards between the layers of the abdominal muscles, in company with branches of the lum bar nerves, and anastomose with the lower in tercostals, mammary, epigastric, and circum flexa The middle sacral artery arises from the back part of the abdominal aorta, immediately above the origins of the primitive iliacs, from one of which it arises in some rare cases, it descends exactly over the middle of the anterior surface of the bodies of the last abdominal vertebra, false vertebrae of the sacrum and os coccygis, lying close on the surfaces of those bones ; the branches which it gives off are distributed in a lateral direction ; the first is the largest and not unfrequently is the fifth lumbar artery, the size of which sometimes exceeds that of the continuation of the trunk of the middle sacral itself. This
branch divides into an anterior and a posterior, the distribution of which is similar to that of the superior lumbar arteries. Two transverse branches usually arise from the middle sacral on the body of each false vertebra ; these pass ing outwards give branches to the periosteum and the substance of the sacrum, anastomose with branches of the lateral sacral arteries, and enter the anterior sacral foramina, where they give some branches to the origins of the sacral nerves, and emerging from the posterior sacral foramina are lost in the muscles arising from the back part of the sacrum ; finally, the middle sacral terminates at the extremity of the coccyx in small branches, which it sends to the rectum and surrounding fat.
The middle sacral artery is sometimes found double ; in the foetus this artery is propor tionally larger than in the adult, especially in the earlier periods of gestation. In some ani mals, the size of the middle sacral artery is scarcely inferior to that of the aorta itself, as in the cetacea and fishes. In all animals fur nished with tails, the size of this artery bears a constant relation to the size of that member.
Aneurism rarely affects any of the branches of the aorta above described ; it, however, occa sionally occurs in the coeliac or mesenteric arte ries, or some of their branches. An interesting case of aneurism of the hepatic artery unat tended by pulsation during life, and which produced jaundice by pressing on the ductus communis choledochus, is reported by Dr. Wil liam Stokes, in the Dublin Journal of Medical and Chemical Science, for July 1834. We once witnessed the dissection of a female aged forty, under the care of the late Professor Todd, in the Surgical Hospital of the House of Indus try in Dublin, in whom three distinct aneurisms of large size were found in the epigastric region ; one of the hepatic artery, which communicated with that vessel by a longitudinal fissure, and which had opened into the cavity of the gall bladder; one of the trunk of the coronary artery of the stomach, and a third of the splenic artery. A remarkable feature in this case, and that of Dr. Stokes, was the absence of pulsa tion during life, in consequence of which the nature of the disease was not discovered until the post-mortem examination ; the above cir cumstance may be attributed to the want of resistance in the surrounding parts, and it is one which frequently obscures the diagnosis of abdominal aneurisms.