58 Charles Reid 



muscle circularly disposed and elastic fibres; towards outer part of media, 

 amongst the circularly disposed plain muscle and elastic fibres irregularly 

 arranged groups of plain muscle, many running longitudinally. 



(3) Wall of abnormal coronary artery. 

 Endothelium, healthy. 



Subendothelial elastic layer, quite well marked. Wall varies in thickness, 

 the thinner parts being at most one-half the thickness of the thicker portions. 



Thicker portions : large amount of plain muscle arranged in bundles; rather 

 granular looking elastic tissue between the bundles — apparently split longi- 

 tudinally in places. 



Thinner portions : much less plain muscle than the preceding; towards the 

 centre of one portion of the media, small oval-shaped area which does not 

 stain well : nuclei stain fairly well but are variable in shape. The elastic tissue 

 apparently shows large coarse granules and it appears to become fragmented 

 transversely into more or less elliptical portions. 



Externa, well marked. 



(4) Wall of dilated portion of abnormal coronary artery. 

 Two layers: (1) External, epicardium; 



(2) Internal, part corresponding to wall of the abnormal 

 coronary artery; practically no plain muscle or elastic fibres; rather de- 

 generate-looking connective tissue showing nuclei which stain fairly well, 

 fibrils, and perhaps "ghost-like" elastic fibres. 



Interior to the above is a fairly thick endothelial and subendothelial layer 

 showing connective tissue and elastic tissue arranged parallel to the inner 

 surface; nuclei stain well. 



Endothelium appears to show proliferation of its cells, the deeper layers of 

 which show signs of organisation. 



(5) Lining of cavity and subjacent myocardium, 

 (a) Endothelium, normal; no proliferation. 



(6) Subendothelial elastic layer, fairly well marked. 



(c) Layer of more or less homogeneous tissue taking up eosin stain, no 

 sign of elastic or muscle fibres. 



(d) More or less continuous layer of about ^th thickness of (c), consisting 

 of heart muscle fibres and white fibrous connective tissue. 



(e) Vascular layer, thinner than (d). 

 ( /') Heart muscle proper. 



(6) Junction of dilated end of abnormal coronary artery with ventricle. 

 Epicardium and wall of distended portion can be seen separated by heart 



muscle; the heart muscle ceases and the epicardium and the wall fuse loosely 

 at first, but firmly within a distance of 2 cm. from the point where the heart 

 muscle ceases ; epicardium at the point where the heart muscle ceases becomes 

 much thinned quite abruptly, and continues thin for about a distance of 



