308 ZOOTOMY. 



XXVI. Dissect away the pericardium, the thymus gland, 

 and any fat about the base of the heart which may 

 obscure the vessels coming from it. Follow r out 

 these vessels to the head and anterior extremities 

 by clearing away the muscle, connective tissue, 

 fat, &c., by which they are surrounded. Also 

 clean the aorta ( 237) and postcaval, and follow 

 out their branches into the posterior extremities, 

 taking care not to injure the ureters ( 262), 

 and the vasa deferentia ( 267) or uteri ( 288). 

 Make out : 



. 224. The left ventricle (Fig. 61, l.v\ which forms the 

 whole apex of the heart : it is lighter in colour than the 

 rest of the organ and harder to the touch. 



225. The right ventricle (r.v), divided by an oblique 

 depression from the left ventricle : it is darker in colour 

 than the left and softer to the touch. 



226. The right and left auricles (r.au, l.au), situated 

 above (anterior to) the corresponding ventricles : they are 

 small, dark, thin-walled chambers, slightly overlapping the 

 bases of the ventricles^ 



227. The ramifications of the coronary artery and 

 vein over the surface of the ventricles. 



228. The bifurcation of the trachea, at about the level of 

 the base of the heart, to form the two bronchi, one of 

 which passes to each lung. 



229. The pulmonary artery (p.a], proceeding from the 

 cone-like anterior prolongation of the right ventricle, and 

 passing forwards and to the left : it soon divides into a right 

 and a left trunk, one of which passes to each lung. 



230. The pulmonary veins (p.v), returning the blood 

 from the lung to the left auricle. They are best seen at a 

 later stage (see 306). 



