THE PIGEON. 237 



XXXVI. Dissect off the pericardium : carefully clear 

 away the connective tissue and fat from the vessels 

 connected with the base of the heart, and trace 

 them out as far as is necessary to verify the 

 following descriptions : make out : 



234. The separation of the heart into an anterior, dark, 

 thin-walled auricular division, and a posterior, lighter 

 coloured, thick-walled ventricular division of a conical 

 shape : the two divisions are separated by a line of fat, 

 which should be carefully removed. 



235. The left ventricle (Fig. 54, l.vri), forming the 

 apex of the heart as well as the left convex side .of the 

 ventricular division : it is very firm and hard to the touch. 



236. The right ventricle (r.vn\ much softer to the 

 touch than the left, and forming the right concave side of 

 the ventricular division. 



237. The right auricle (r.au), forming the right half of the 

 auricular division, and usually gorged with blood after death. 



238. The left auricle (l.au), usually in a more collapsed 

 state than the right. 



239. The innominate arteries (in.a), two large trunks 

 apparently proceeding from the centre of the base of the 

 heart, and diverging from one another like the limbs of a V : 

 each passes forwards and outwards, and divides into two 

 arteries, the common carotid (c.c), which proceeds almost 

 directly forwards, and the subclavian (scl.d), which con- 

 tinues the directibn of the innominate, and almost immediately 

 divides into two : of these the brachial or axillary artery 

 (br.a) passes forwards and outwards, and curving round 

 at the shoulder enters the wing, which it supplies, 1 while 



1 If the muscles are to be dissected in the same specimen, defer tracing 

 the blood-vessels of the wing until its muscles are examined (see 

 320327). 



