386 DISSECTION OF THE THORAX. 



to the lobule. At the lobule the arterial branch is minutely subdivided, 

 and its ramifications enter the interlobular fissure to end in the cell wall 

 in the following way: Over the bottom of the cell they form a very fine 

 capillary network, but at the circumference they give rise to a circular 

 vessel; and the circles of several cells communicate with each other. 



The pulmonary veins begin in the vascular network before mentioned. 

 The twigs issuing from the several lobules are destitute of valves, and are 

 united in larger tubes which course to the root of the lung. Although the 

 small lobular branches of the arteries remain separate from one another, 

 the corresponding veins anastomose together. 



The bronchial arteries enter the lung on the air tube, and supply deep 

 branches to it and the contiguous glands, to the large bloodvessels, and to 

 the interlobular areolar tissue of the lung. On the smallest air tubes 

 minute branches anastomose with offsets of the pulmonary arteries. 



Superficial tortuous offsets of the artery ramify beneath the pleura, form- 

 ing a capillary network. 



The bronchial vein begins by twigs corresponding with the superficial 

 and deep branches of the artery. Leaving the lung at the root, the vein 

 ends differently on opposite sides of the body (p. 337). 



Nerves and lymphatics. The lung receives nerves from the vagus and 

 the sympathetic ; and the offsets follow the branches of the air tube, but 

 their ending is uncertain. Remak describes small ganglia on the sympa- 

 thetic filaments. The lymphatics of the lung are both superficial and deep, 

 and enter the bronchial glands at the root of the lung. 



PARTS ON THE SPINE AND THE SYMPATHETIC CORD. 



In front of the spinal column are the several parts lying in the inter- 

 pleural space of the posterior half of the mediastinum, viz., the aorta, 

 azygos veins, thoracic duct, oesophagus, and splanchnic nerves. 



Dissection. The thoracic duct should be found first near the diaphragm 

 by removing the pleural ; there it is about as large as a crow quill, and 

 rests against the right side of the aorta : this slender vessel may be in- 

 jected with tallow. 



The areolar tissue and the pleura are to be cleared away from the dif- 

 ferent parts before mentioned ; and the azygos or intercostal veins, one on 

 the right and two on the left aorta, should be dissected. Next follow the 

 thoracic duct upwards beneath the arch of the aorta, and along the reso- 

 phagus beneath the pleura, till it leaves the upper aperture of the thorax. 



After raising the pleura also from the inner surface of the chest, the 

 ganglia-ted cord of the sympathetic nerve will be seen lying over the heads 

 of the ribs. Branches are to be followed outwards from the ganglia to the 

 intercostal nerves ; and others inwards over the bodies of the vertebrae, 

 the lowest and largest of these forming the three trunks of the splanchnic 

 nerves. 



The DESCENDING THORACIC AORTA is the part of the great systemic 

 vessel above the diaphragm. Its extent is from the lower border of the 

 fifth dorsal vertebra (the left side), where the arch ceases, to the front of 

 the last dorsal vertebra. 



Contained in the interpleural space in front of the spine, the vessel is 

 rather curved, lying at its upper part on the left, but below on the front 

 of the spinal column. Beneath it are the vertebrae and the smaller azygos 

 veins. In front of the vessel is the root of the left lung with the peri car- 



