THE HEART. 



587 



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

 separated from it at its periphery by the horizontal groove {aimculo-vmtricular 

 groove) of the heart. 



3. Inteknal Conformation of the Heart (Figs. 351, 352, 358). 



Preparation.— It sufBces 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 this organ is often necessary in 

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

 these cavities. The riglit auricle is prepared by making a transverse incision along its ventri- 

 cular margin, from the appendix tu its right border, and crossed by a perpendicular incision, 

 carried from the si<]e of the anterior to the pos- 

 terior cava. The right ventricle is laid open by Fig. 351 

 making an incision parallel with, and u 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 midille line 

 behind to the auric ulo- ventricular opening. 

 The interior of the left auricle is expn^ed by 

 a J_ -shaped 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 coutiuuing it 

 around the apex of the heart to the auriculo- 

 ventricular opening behind.) 



If the heart, when viewed externally, 

 appears to be a simple organ, it is not 

 so when examined internally. The 

 vertical septum which divides it into 

 two bil ocular cavities, in reality makes 

 two hearts of it — one for the dark, the 

 other for the red blood. We will suc- 

 cessively study these two cavities, by com- 

 mencing with the partition that separates 

 them. 



A. Cardiac Septum. — The superior 

 part of this septum, between the two 

 auricles, is named the inter-auricular 

 partiUon {septum anricularum). The 

 inferior portion constitutes the inter- 

 ventricular partition {septum ventricu- 

 lorum). The first— thin and not exten- 

 sive — 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 tliis portion are situated in front and to the right. They are indifferently 

 named the anterior or right cavities of the heart — the latter term being in general 

 use, though the first is much more convenient in Veterinary Anatomy. 



Right Ventricle. — The right ventricle represents a hollow cone, a 

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

 into the cavity by the left ventricle. 



RIGHT SIDE OF THE HEART LAID OPEN, 



1, Cavity of right auricle ; 2, appendix auri- 

 culae, with musculi pectinati ; 3, anterior 

 vena cava opening into the upper part of 

 the right auricle ; 4, posterior vena cava ; 

 5, fossa ovalis, surrounded by the annulus 

 oralis ; 6, Eustachian valve ; 7, opening of 

 the coronary sinus ; 8, coronary valve ; 9, 

 entrance of auricular-ventricular opening. 

 a, Right ventricle ; 6, its cavity ; c, conus 

 arteriosus, or infundibulum ; d, pulmonary 

 artery ; e, f, tricuspid valve ; g, one of the 

 musculi papillares to which the curtains of 

 the tricuspid valve are attached by chordae 

 tending ; h, columnse carneue ; i, two mus- 

 culi papillares of valvular curtain ; /, I, 

 chord* tendinese; m, .semilunar valves of 

 pulmonary artery ; n, apex of left appendix 

 auriculae ; o, left ventricle. 



