494 ARTERIES. 



The digital arteries at first lie superficial to the flexor tendons, but as they pass 

 forwards with the digital nerves to the clefts between the fingers, they lie be- 

 tween them, and are there joined by the interosseous branches from the deep 

 palmar arch. The digital arteries on the sides of the fingers lie beneath the 

 digital nerves ; and, about the middle of the last phalanx, the two branches for 

 each finger form an arch, from the convexity of which branches pass to supply 

 the matrix of the nail. 



THE DESCENDING AORTA. 



The Descending Aorta is divided into two portions, the Thoracic, and Abdomi- 

 nal, in correspondence with the two great cavities of the trunk in which it is 

 situated. 



The Thoracic Aorta commences at the lower border of the fourth dorsal ver- 

 tebra, on the left side, and terminates at the aortic opening in the Diaphragm, 

 in front of the last dorsal vertebra. At its commencement, it is situated on the 

 left side of the spine ; it approaches the median line as it descends ; and, at its 

 termination, lies directly in front of the column. The direction of this vessel 

 being influenced by the spine, upon which it rests, it describes a curve which 

 is concave forwards in the dorsal region. As the branches given off from it 

 are small, the diminution in the size of the vessel is inconsiderable. It is con- 

 tained in the back part of the posterior mediastinum, being in relation, in front, 

 from above downwards, with the left pulmonary artery, the left bronchus, the 

 pericardium, and the oesophagus; behind, with the vertebral column, and the 

 vena azygos minor ; on the right side, with the vena azygos major, and thoracic 

 duct; on the left side, with the left pleura and lung. The oesophagus, with its 

 accompanying nerves, lies on the right side of the aorta above: in front of the 

 artery, in the middle of its course ; whilst, at its lower part, it is on the left side, 

 on a plane anterior to it. 



PLAN OF THE RELATIONS OF THE THORACIC AORTA. 



In front. 



Left Pulmonary artery. 

 Left Bronchus. 

 Pericardium. 



(Esophagus. 



Riglit side. / \ Left side. 



(Esophagus (above). l Thoracic \ Pleura. 



Vena azygos major. 1 Aorta. ) Left lung. 



Thoracic duct. V / (Esophagus (below). 



Behind. 



Vertebral column. 

 Vena azygos minor. 



Surgical Anatomy. The student should now consider the effects likely to be produced by 

 aneurism of the thoracic aorta, a disease of common occurrence. When we consider the great 

 depth of the vessel from the surface, and the number of important structures which surround it 

 on every side, it may be easily conceived what a variety of obscure symptoms may arise from 

 disease of this part of the arterial system, and how they may be liable to be mistaken for those 

 of other affections. Aneurism of the thoracic aorta most usually extends backwards, along the 

 left side of the spine, producing absorption of the bodies of the vertebrae, with curvature of the 

 spine ; whilst the irritation or pressure on the cord will give rise to pain, either in the chest, 

 back, or loins, with radiating pain in the left upper intercostal spaces, from pressure on the 

 intercostal nerves; at the same time, the tumor may project backwards on each side of the spine, 

 beneath the integument, as a pulsating swelling, simulating abscess connected with diseased bone; 

 or it may displace the oesophagus, and compress the lung on one or the other side. If the tumor 

 extend forward, it may press upon and displace the heart, giving rise to palpitation and other 

 symptoms of disease of that organ ; or it may displace, or even compress, the oesophagus, caus- 

 ing pain and difficulty of swallowing, as in stricture of that tube, and ultimately even open into 

 it by ulceration, producing fatal hemorrhage. If the disease make way to either side, it may 



