124 THE ANATOMY OF THE HORSE. 



groove. The terminal twigs of the vertical branch enter the heart 

 a little above the apex ; the horizontal branch reaches as far as the 

 posterior border of the heart. 



The Left Coronary Artery passes outwards and to the left, between 

 the pulmonary artery and the left auricular appendix. Reaching the 

 aviriculo-ventricular furrow at this point, it divides into a vertical and a 

 horizontal branch. The former descends in the left ventricular furrow ; 

 the latter turns backwards along the auriculo-ventricular furrow. The 

 terminal portion of the vertical branch turns round the anterior border 

 of the heart, and ends in twigs that enter the ventricular wall on the 

 right of its apex ; the horizontal branch terminates in the same way 

 near the posterior border of the heart. 



The corresponding branches of the right and left arteries, thus, approach 

 each other at their terminations, but they do not anastomose ; nor is 

 there any anastomosis between the arteries through their collateral 

 branches. Still more, there is no anastomosis between the adjacent 

 collateral branches of the same coronary artery. * 



The Coronary Veins. — These arise from the capillaries of the coronaiy 

 arteries. The principal vessel of the right side ascends in the right 

 ventricular groove, and at the auriculo-ventricular ftirrow it joins the 

 main vein of the left side. The latter ascends at first in the left ventri- 

 cular furrow, at the top of which it enters the auriculo-ventricular 

 groove. Along this it is reflected backwards ; and turning round the 

 posterior border of the heart, it joins the right vein. The dilated vessel 

 resulting from this union is termed the coronary venotis sinns, and it 

 opens into the right auricle, beneath the mouth of the posterior vena 

 cava. 



For the most part, the veins arising in the wall of the right auricle 

 do not join the large coronary veins, but open into the cavity indepen- 

 dently, by minute mouths — the foramina Thebesii. 



The Nerves of the Heart have already been described (pages 110 and 

 117). In the heart of a lean subject long filaments are visible without 

 dissection, descending beneath the serous covering. 



The Interior of the Heart. — The cavities of the heart should be 

 studied in the order in which the blood passes through them, and 

 therefore the right auricle fixlls to be examined first. The termina- 

 tions of the anterior and posterior cavse and vena azygos (provided 

 that has an independent opening) should be identified ; and then an 

 incision should be made along the wall of the sinus venosus, from 

 the opening of the anterior to that of the posterior cava. Another 

 incision should be carried from this one to the point of the auricula ; 



* Percivall, Leyh, Chfinveau, and all the other authors that I am acquainted with state that the 

 coronary arteries anastomose with one another. That they do not, I have reijeatedly proved by 

 injecting one of them, by wlijch method none of the injection, however fine, can be driven into tlie 

 other artery. 



