66 DR. N. H. ALCOCK ON THE VASCULAB [Feb. 1, 



in the thorax, the apex extending posteriorly and to the left. 

 Clothing the surface is the serous layer of the pericardium ; and 

 it is noticeable that the deposit of fat, so often observed in man, 

 is entirely absent here. In the groove between the right auricle 

 and the aorta is a small portion of the so-called thymus gland. 



Fully three-fourths of the ventral surface is formed by the ven- 

 tricles, little more of the right auricle than the appendix being 

 seen from this aspect, and but the extreme tip of the appendix 

 of the left auricle, appearing under cover of the left precaval vein. 

 Of the ventricular part, three-fifths are formed by the right ventricle, 

 the remainder, including the apex, by the left. " (Fig. 1, p. 63.) 



On the dorsal surface of the heart the ventricles occupy scarcely 

 one half, the auricles, with the much expanded transverse part of 

 the left precaval vein, forming the remainder. (Fig. 4.) 



The Right Auncle is composed of appendix and atrium, separated 

 externally by a well-marked sulcus. In the specimens I have 

 examined it was much distended with clotted blood, so that it 

 appeared considerably more capacious than the left auricle. More 

 of the right aui'icle also appears on the surface than the left, the 

 latter being concealed by the left precaval vein and the pulmonary 

 artery with its branches. 



Fig. 4. 



Heart of Pteropus meditts, dorsal surface, x2. — TE. Pretracheal branch 

 from base of left common carotid artery. L.P.A. Left Pulmonary Artery. 

 Other letters as in fig. 1. 



The wall of the right auricle is thin, and on opening the cavity 



