THE VESSELS. 321 



phagus (above), Ven. azygos and duct, thoracicus close to it (above, 

 where it winds to the left, behind it) ; is surrounded by much adi- 

 pose tissue, and many lymphatic glands. Branches : 



1. Arlt, bronchioles, two to the left, one to the right ; they arise sometimes 

 from a common trunk, from the anterior wall of the aorta (also from mam- 

 mar, interna or subclavia), and pass forwards to the posterior wall of the 

 bronchus, ramifying on the bronchia and pulmonary vesicles; they give 

 branches to the oesophagus; bronchial glands, and anastomose with the coro- 

 nary arteries of the heart and thyreoidea inferior. 



2. CEsophagea, five to seven, thin and long, arising in front from the aorta; 

 they pass to the anterior surface of the cesophagus, in the mucous membrane 

 of which they terminate, and send long branches upwards and downwards. 



3. Mediastince posticcs, small branches for the posterior wall of the pericar- 

 dium and the mediastina. Two phrenicte superiores arise deeply, pass to the 

 internal crura of the diaphragm, and anastomose with the oesophagece. 



4. Intercostales posteriores, eight to nine for the second, or third to eleventh 

 intercostal space (the first and second are supplied by intercostal, prima. See 

 subclavia). Origin : from the lateral walls of the aorta ; the superior at an 

 acute, the inferior at a right angle. Course : the superior upwards, the infe- 

 rior more horizontally outwards, over the heads of the ribs into the intercostal 

 space next above, and divided between the heads of the two ribs into ram. an- 

 terior and posterior. Situation : behind the pleura and the trunk of sympathi- 

 cus; the right behind the cesophagus, ductus thoracicus; and Ven. azygos also ; 

 the left behind v. hemiazygos and sympathicus; the two last (right and left) co- 

 vered by the crura of the diaphragm. 



Branches : besides many small osseous branches for the bodies of the ver- 

 tebrae, the following: 



a. Ramus anterior s. intercostalis , passes in the direction of the trunk, in the 

 centre of the intercostal spaces, at first between pleura and m. intercost. 

 intern., then between intern, and extern., and there divides into: 



1. Ham. sup. s. infracostalis , the continuation of the trunk which passes 

 on the inferior border of the rib situated above, in a proper groove, 

 as far as the anterior third, then in the middle of the intercostal space, 

 descending and anastomosing with a. mammar. intern., epigastrica, 

 phrenica, circumflexa ilei. 



2. Ram. inferior, supracostalis, which passes to the superior border of 

 the rib lying below, and is lost in the periosteum and the muscles. 



b. Ramus posterior s. dorsalis; passes between process, transversi, on the 

 external border of lig. colli costce intern, backwards, and divides into : 



1. Ram. spinalis, which passes through foram. intervertebrale, with a 

 branch for the body of the vertebra, with another for the medulla spin. 



2. Ram. muscularis, a larger branch, which ramifies between longissim. 

 dorsi and ileocostalis, and is lost in the skin. 



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