136 THE POSTERIOR AORTA. 



2 . 7) also connects the basilar with the posterior transverse 

 {Plate V. Fig 2 . a) ; which, beside giving off several branches, 

 transmits two large trunks, called the right and left laterals 

 {Plate V. Fig 2 . c, d) ; and these, uniting with the ante- 

 rior transverse artery, form the circulus arteriosis, at the 

 very base of the brain {Plate V. Fig 2 . a, b, c, d). 



The internal carotids, having entered the cranium, unite 

 with the circulus arteriosis, at the base of the crura cerebri ; 

 which gives off, just afterwards, the ophthalmus, or central 

 artery of the retina {Plate V. Fig 2.9,9). These last, how- 

 ever, do not in any two subjects appear to originate exactly in 

 the same place. The circuhis arteriosis sends off two large 

 trunks; named the middle cerebrals (Plate \. Fig 2 .11, 

 11) ; after which, directly in front, it dispatches one trunk, 

 called the anterior cerebral {Plate V. Fig 2 . 12) ; and this 

 subsequently dividing, forms the right and left anterior cere- 

 bral {Plate V. Fig 2 . 13, 13). Thus the brain is amply 

 supplied with blood ; but whoever inspects the plate so often 

 referred to, must be struck with the very tortuous or crooked 

 course which one and all of these vessels take. The reason 

 of this is obviously to check the impetuosity of the arterial 

 current ; but, notwithstanding all the care nature takes to 

 prevent it, cases of congestion do occur. 



THE POSTERIOR AORTA. 



This large and important vessel {Fig 13.4. Plate IV. A) 

 furnishes blood to all the parts of the body, save the head, 

 neck, and fore limbs. It curves upwards and backwards, 

 inclining in its course to the left side of the vertebrae ; and 

 supplies all but the first four or five ribs. In the thoracic 

 passage of the aorta it gives off the bronchial {Fig 13.5); 

 the oesophageal {Fig 13 . 6, 6) ; and the intercostals {Fig 

 13.7); and as it enters the abdomen between the crura of the 

 diaphragm, it leaves the phrenic {Fig 13 . 8). The coeliac 

 {Fig 13 . 9) is often the first true abdominal branch of the 

 aorta, and, in most instances, is the common trunk of the 

 splenic {Fig 13 . a); gastric {Fig 13 . b) ; and hepatic {Fig 

 13 . d) arteries. The gastric divides into two branches; one 

 of which spreads its ramifications over the lesser curvatures 

 of the stomach, upon the upper surface ; and the other joins 

 the splenic, and becomes the left gastric. The hepatic 



