520 THE ABTEBIES. 



intercostals and tlie Twoncliial and oesophageal arteries, when its volume is 

 very considerable. It is much smaller when it only gives oif the second 

 pair of intercostals, which is sometimes the case. 



2. Lumbar Arteries. 



These are five or six in number, and do not differ in their general 

 arrangement from the intercostal arteries ; they having the same mode of 

 origin, the same division into two branches, and the same distribution. The 

 superim; or lumho-spinal branch, is much larger than the inferior, and goes to 

 the muscles and integuments of the lumbar region ; it also furnishes a 

 branch to the spinal cord. The inferior branch passes above the large and 

 small psoas muscles, giving them numerous twigs, and extending to the 

 muscular portions of the transverse and small oblique abdominal muscles, 

 where their ramifications anastomose with those of the circumflex iliac 

 artery. 



The last, and sometimes also the second-last lumbar artery, arises from 

 the internal iliac trunk ; the others emerge directly from the abdominal 

 aorta. 



3. Diaphragmatic (or Phrenic) Arteries. 



These are two or three small vessels which spring from the aorta as it 

 passes between the two pillars of the diaphragm, and are destined for that 

 muscle. The left pillar receives a very insignificant branch ; but the right 

 has two, the most considerable of which is alone constant ; it sometimes sends 

 subpleural ramuscules to the right lung. 



4. Middle Sacral {Sacra Media) Artery. 



This vessel is often absent, and when it exists is very variable in size, 

 though always extremely slender. It arises from the terminal extremity of 

 the aorta, in the re-entering angle comprised between the two internal iliac 

 arteries, and is carried to the inferior face of the sacrum, where it is 

 expended in lateral ramifications which go to the periosteum. It has been 

 thought necessary to notice this artery, as it attains a considerable volume 

 in Man and some animals, and continues the aortic tree beneath the sacral 

 portion of the vertebral column. 



VISCERAL BEANCHES OF THE POSTEEIOE AOETA. 



1. Broncho-oesophageal Trunk. 



Destined for the lung, the visceral pleura, the mediastinum, and the 

 oesophagus, this artery arises, not, as is generally said, in the concavity of 

 the arch of the aorta, but opposite to it, and very near, but to the right 

 of, the first pair of intercostals ; often even in common with these arteries 

 and with the second pair.' After leaving the aorta, it insinuates itself 

 between that trunk and the oesophagus, and above the bifurcation of the 

 trachea divides into branches, the bronchial arteries. In its short course it 

 gives off the two oesophageal arteries and a certain number of innominate 

 ramuscules. 



Beonohial Aetebies.— The disposition of these two vessels is extremely 

 simple ; they enter the lung with the bronchi, one to the right, the other to 

 the left, and there break up into arborescent ramifications which follow the 

 air-tubes to the pulmonary lobules. 



CEbophageal Arteries. — These two arteries are placed in the posterior 

 ' See Intercostals. 



