STRICTURE AND OBLITERATION OF THE AORTA. 427 



recovei y from this condition is possible. Far more frequently, in the 

 course even of a few hours or days, death ensues from bursting of the 

 adventitia, and escape of the blood into the pericardium, mediastinum, 

 or pleura. At the moment of rupture the patient sometimes suffers 

 violent pain ; but soon becomes pale, cold, and pulseless, singultus 

 appearing with profound syncope, and other symptoms of internal 

 haemorrhage. 



CHAPTER IV. 



STRICTURE AND OBLITERATION OF THE AORTA. 



ACCORDING to Rokitansky^ congenital narrowness of the aortic 

 system is sometimes found, and principally in the female sex. It is 

 accompanied by pallor, tendency to syncope, retarded development of 

 the entire frame, but especially of the sexual organs, symptoms simi- 

 lar to those which attend congenital smallness of the heart. 



We sometimes see a partial contraction of the aorta as a persist- 

 ence of the so-called isthmus aortae at a point between the left sub- 

 clavian and the ductus Botalli. In other instances there is an obliter- 

 ation of the vessel at this point instead of a contraction. In these 

 cases we have no sufficient knowledge of the conditions occasioning 

 the permanent narrowness, or even obliteration of the isthmus aortae, 

 which exists during foetal life as a narrow communication between the 

 arch and the descending aorta, but which becomes dilated soon after 

 birth. It has been supposed that the ductus arteriosus Botalli might 

 become obstructed by a thrombus, and that this thrombus might ex- 

 tend into the aorta ; or that the ductus Botalli, while in process of 

 obliteration, might, during its contraction, also constrict the aorta. 

 Neither explanation is satisfactory, as both constriction and oblitera- 

 tion of the aorta have been observed where the duct of Botalli re- 

 mained open. 



The immediate consequence of contraction of the aorta is hyper- 

 trophy of the left ventricle and dilatation of that part of the aorta 

 which lies between the heart and the point of constriction. The enor- 

 mous dilatation which takes place in the branches of the subclavian, 

 and its anastomoses with the intercostal arteries, are of great impor- 

 tance. The finest ramifications are converted into large branches with 

 firm walls, and a collateral circulation so complete is set up, that the 

 blood, in ample quantity, is conveyed around the seat of stricture into 

 the descending aorta. The principal of these collateral channels is 

 formed by anastomosis between the first intercostal, arising from the 

 subclavian, and the second, which springs from the descending aorta ; 

 but extensive anastomotic communication also forms from the dorsalis 



