THE HEART. 503 



The left face, concave from before to behind, includes the arterial trunks 

 which leave the base of the heart. 



Each of the extremities, anterior and posterior, constitutes a detached 

 portion, named the appendix auricularis ; these appendages are curved 

 towards each other in being flattened from above to below. Their convex 

 border is more or less crenelated, like the margin of a cock's comb, and their 

 culminating portion advances nearly to the pulmonary artery, above the 

 trunk of the cardiac vessels (Fig. 258). 



The base of the auricular mass, opposed to the base of the ventricles, 

 is separated from it at its periphery by the horizontal groove of the heart. 



3. Internal Conformation of the Heart. 



Preparation. It suffices to make a longitudinal incision before and behind the organ, 

 in order to expose its cavities. (I have followed Wilson's directions for many years when 

 examining the interior of the heart, and as a careful inspection of it is often necessary in 

 the course of an autopsy, I think tlie student should practise the best method of laying 

 open these cavities. Tne right auricle is prepared by making a transverse incision along 

 its ventricular margin, from the appendix to its right border, and crossed by a perpendi- 

 cular incision, carried from the side of the anterior to the posterior cava. The right 

 ventricle is laid open by making an incision parallel with, and a little to the right of, the 

 middle line, from the pulmonary artery in front, to the apex of the heart, and thence by 

 the side of the middle line behind to the aurk-ulo-ventricular opening. The interior of 

 the left auricle is exposed by a _[.' sua P ei ' incision, the horizontal section being made 

 along the border which is attached to the base of the ventricle. The latter is opened by 

 making an incision a little to the left of the septum ventriculorum, and continuing it 

 around the apex of the heart to the auriculo-ventricular opening behind.) 



If the heart, when viewed externally, appears to be a single organ, it is 

 not so when examined internally. The vertical septum which divides it 

 into two bilocular pouches, in reality makes two hearts of it one for the 

 dark, the other for the red blood. We will successively study these two 

 cavites by commencing with the partition that separates them. 



A. CARDIAC SEPTUM. The superior part of this septum, placed between 

 the two auricles, is named the interauricular partition (septum auricularum). 

 The inferior portion constitutes the interventricular partition (septum ven- 

 triculorum). The first, thin and not extensive, is perforated in the foetus by 

 the foramen of Botal (foramen ovale). The second, thick in its centre, thins 

 a little towards its borders. 



B. DARK-BLOOD (or PULMONARY) HEART. The two superposed cavities 

 forming this pouch are situated in front and to the right. They are indif- 

 ferently named the anterior or right cavities of the heart : the latter term 

 being in most general use, though the first is much more convenient in 

 Veterinary Anatomy. 



RIGHT VENTRICLE. The right ventricle represents a hollow cone, the 

 horizontal section of which resembles a crescent, its posterior plane being 

 pushed into the cavity by the left ventricle. 



It oifers two walls, an- apex, and a base. 



Walls. The anterior wall is concave ; its thickness is more considerable 

 above than below, and averages 6-10ths of an inch. The posterior wall is 

 convex, and formed by the septum ventriculorum. 



Both walls are uneven, from the presence of fleshy columns (columnse 

 carnese), which we will commence examining in a general manner, as they are 

 found in the four compartments of the heart. They are of three kinds : 

 one kind, named the pillars of the heart (columnae or musculi papillares), thick 

 and short, and fixed by their base to the walls of the ventricles, have a free 



