ABNOKMALITIES OF AETEEIES. 1053 



being given to the second intercostal space, which is usually supplied by the superior intercostal 

 artery ; this is brought about by. the persistence of the root of the tenth somatic intersegmental 

 artery and the disappearance' of the precostal anastomosis between the ventral branches of the 

 ninth and tenth somatic intersegmental arteries. Very rarely the first aortic intercostal artery 

 sends a branch upwards between the necks of the ribs and the transverse processes of the upper 

 thoracic region ; this branch supplies the upper intercostal spaces, the superior intercostal artery 

 being small or absent, and it terminates by becoming the profunda cervicis artery. It is due to 

 the persistence of the postcostal anastomoses in the upper thoracic region, and is a repetition of a 

 condition regularly present in some carnivores. 



There are no very important variations of the cesophageal, pericardial, and mediastinal 

 arteries. 



Lumbar Arteries. Variations of the lumbar arteries are very similar to those of the 

 intercostal arteries, and they are due to similar causes. The lumbar arteries of opposite sides 

 may arise by common stems from the back of the aorta ; and the last pair of lumbar arteries 

 may arise in common with the middle sacral artery. Further, a lumbar artery may have its 

 area of distribution extended into the adjacent segment. 



The inferior phrenic arteries are very variable ; they may arise by a common trunk either 

 from the cceliac artery or from the aorta ; they may arise separately either from the aorta or 

 from the coeliac artery and more commonly from the latter vessel ; or again, one may spring 

 from the aorta or cceliac artery, and the other from the coronary, renal, or even from the 

 superior mesenteric artery. 



The middle sacral artery usually springs from the back of the aorta above its bifurcation ; 

 it may be considerably above, or more rarely it may spring directly from the bifurcation. Not 

 infrequently it arises from the last lumbar artery or from a stem common to the two last 

 lumbar arteries, and occasionally it arises from a common or internal iliac artery. Some- 

 times it gives off the last pair of lumbar arteries, and, in a few cases, an accessory, renal, or a 

 haemorrhoidal branch arises from it. The vessel is not always present, it may be double, 

 entirely or in part, and it may bifurcate at its termination. 



The renal arteries frequently deviate from the normal arrangement. The arteries of 

 opposite sides may spring from a common stem, or there may be two or more renal arteries on 

 one or both sides. The accessory arteries are more common on the left than on the right side, 

 and an accessory artery arising below the ordinary vessel is more common than one arising 

 above it. 



Accessory renal arteries may be derived not only from the aorta, but also from the common 

 iliac or hypogastric arteries ; they have been described as arising also from the inferior phrenic, 

 spermatic, lumbar, or middle sacral arteries,, and even from the external iliac artery. As the 

 kidney is developed in the region of the first sacral vertebra, and afterwards ascends to its perma- 

 nent position, it is not surprising that it occasionally receives arteries from the main stem of 

 more than one of the segments of the body through which it has passed, and it is usually found 

 that the lower the position of the kidney in the abdomen the more likely it is to receive its 

 arteries from the lower part of the aorta or from the common iliac arteries. The accessory renal 

 arteries which spring from the inferior phrenic, the spermatic, and lumbar arteries can only be 

 the result of the persistence and enlargement of anastomosing channels between the renal and 

 either another intermediate visceral, or a somatic artery. 



The testicular or ovarian arteries may be double on one or both sides ; the arteries of the 

 two sides may spring from a common trunk, or each may arise from the renal, accessory renal, 

 or suprarenal arteries. The right artery may pass behind instead of in front of the inferior 

 vena cava. The spermatic and ovarian arteries arise from the upper lumbar portion of the 

 aorta, because the testes and ovaries are developed in and obtain their arterial supply in that 

 region, and the vessels are elongated as the testes and ovaries descend to their permanent 

 positions. The occurrence of two spermatic arteries on one side is probably an indication that 

 the testis was developed in two segments of the body. The origin of a spermatic artery from a 

 renal or suprarenal artery is due to the obliteration of the root of the original vessel and the 

 enlargement of an anastomosis between the intermediate visceral arteries of adjacent segments. 



The cOBliac artery may be absent, its branches arising separately from the aorta or from some 

 other source. Sometimes it gives off only two branches, usually the left gastric and splenic, and 

 occasionally it gives four branches, the additional branch being either a second left gastric artery 

 or a separate gastro-duodenal artery. 



The hepatic artery may spring directly from the aorta or from the superior mesenteric 

 artery, and the left hepatic artery arises occasionally from the left gastric artery. Accessory hepatic 

 arteries are not uncommon, and they originate either from the left gastric, superior mesenteric, 

 renal, or inferior mesenteric artery. 



The left gastric artery is occasionally double ; it may spring directly from the aorta, and it 

 may give off the left hepatic or an accessory hepatic artery. 



The splenic artery may arise from the middle colic, from the left hepatic, or from the 

 superior or inferior mesenteric artery. 



The superior mesenteric artery may be double, and it may supply the whole of the 

 alimentary canal from the second part of the duodenum to the end of the rectum, the inferior 

 mesenteric artery being absent. In addition to its ordinary branches it may give off a hepatic, 

 a splenic, a pancreatic, a gastric, a gastro-epiploic or a gastro-duodenal branch. Very rarely 

 "* gives off an omphalo -mesenteric branch, which passes to the region of the umbilicus and 

 es connected with capillary vessels in the falciform ligament of the liver. 



