Abnormal Left Coronary Artery of Ox Heart 55 



Further dissection showed that this abnormal vessel arose about 1-25 cm. 

 above the middle of the left posterior cusp of the aortic valve. The tip of the 

 middle finger could be inserted into the vessel at its origin. A coronary artery, 

 smaller in size, arose above the anterior cusp, but no artery arose above the 

 right posterior cusp. In the normal ox heart the calibres of the two coronaries 

 differ considerably, the left being the larger, but the normal left coronary 

 artery did not admit the tip of the middle finger. 



No other abnormal opening was noted at the base of the aorta. The aortic wall 

 was healthy and the aortic valves appeared healthy, and, when tested by means 

 of a stream of water directed into the cut end of the aorta, proved competent. 



The abnormal vessel passed forward between the left auricular appendix 

 and the pulmonary artery. The first branch came off the main vessel about 

 3*5 cm. from the cusp, and ran transversely outwards in the left auriculo- 

 ventricular groove. Its calibre appeared similar to that of the normal right 

 coronary artery. This branch was evidently the transverse branch of the left 

 coronary artery and was of normal size. 



The abnormal vessel passed along the interventricular septum giving off 

 numerous small branches to the septum without any marked diminution in 

 calibre until it reached just above the apex of the left ventricle anteriorly 

 where it dilated into a cyst-like structure roughly conical in shape with its 

 base anterior and its apex on a level with the inner surface of the left ventricle. 

 With regard to the dimensions of the above structure, the diameter of the 

 base of the cone was about 7 cm. while the height of the cone was about 

 6 cm. It will be noted that the height of this structure is practically equal to 

 the thickness of the wall of the left ventricle. 



The wall of the cone-shaped structure appeared similar in structure to the 

 wall of the abnormal vessel but slightly thinner. It was lined by smooth 

 endothelium, and its base was quite uncovered by cardiac muscular fibres, 

 being apparently in direct relationship with the pericardium. The rest of the 

 wall of the cone-shaped structure was attached firmly to the muscle of the 

 left ventricle throughout its entire thickness. 



The walls of the abnormal vessel and the dilated portion were apparently 

 continuous. Anteriorly, where the wall of the dilated portion was not attached 

 to the wall of the ventricle, the epicardium passed directly on to the wall of 

 the dilated portion. At first, the union was not firm, the two being held to- 

 gether by loose tissue, but at a distance of about 2 cm. from the place where 

 the ventricular muscle became deficient the wall of the dilated portion and 

 the epicardium became fused apparently into one. 



The cavity communicated directly with the left ventricle near its apex by 

 a circular aperture, which was sufficiently large to admit the middle finger, 

 and was guarded by a valve-like structure. Examination showed that the 

 latter consisted of : 



(1) an inner fibrous ring, diameter 1'5 cm., forming the circumference of 

 the aperture, 



