THE UEABT. 



587 



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

 separated from it at its periphery by the horizontal groove {aurkulo-ventricular 

 groove) of the heart. 



'^. LvTERNAL Conformation of the Heart (Figs. 351, 352, 353). 



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

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

 examining the iuterioi-of the heart, and as a careful inspection of this organ is often neci ssary in 

 the course of an autojisy, I think tlie student sliould practise the best metliod of laying open 

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

 cular margin, from the iippeudix to its right border, and crossed by a perpeudicular incision, 

 carried from the side of the anterior to the pos- 

 terior cava. The right ventri -le is laid open by 

 making an incision parallel with, and a little 

 to the right of, the middle line, from the 

 pulmonaiy artery in front, to the apex of the 

 heart, and thence by the side of the middle line 

 behind to the auriculo-ventricular opening. 

 The interior of the left auricle is exposed by 

 a _L-8haped 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 veutriculorum, and continuing it 

 around the apex of the heart to the auriculo- 

 ventricular opening behind.) 



If the heart, when viewed externally, 

 ap})ears to be a simple organ, it is not 

 so when examined internally. The 

 vertical septum which divides it into 

 two bilocular 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-aurHcidar 

 partition (spptum auricularum). The 

 inferior portion constitutes the inter- 

 ventrindnr partition {f^eptvm ventricu- 

 Jorum). The first — thin and not exten- 

 sive — is perforated in the foetus by the 



foranmi 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 portion are situated in front and to the right. They are indifferently 

 named the anterior or right cavitiei^ 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, appendi.x auri- 

 culae, with musculi jiectinati ; 3, anterior 

 vena cava opening into the upper part of 

 the right auricle ; 4, posterior vena cava ; 

 5, fossa ovalis, surroinided bv the annujus 

 ovalis ; 6, Eustachian valve ; 7, opening of 

 the coronaiy sinus; 8, coronarv valve; 9, 

 entrance of nuricular-ventricular opening. 

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

 arteriosus, or infundibuluni ; d, pulmonary 

 artery; e, f, tricuspid v.ilve ; g, one of the 

 musculi papillares to which the curtains of 

 the tiicuspid valve are attached by chordae 

 tendinte ; A, columnar carnea? ; i, two mus- 

 culi papillares of valvular curtain ; /, /, 

 chor<la> tendinea?; m, semilunar valves of 

 pulmonary artery ; n, ai)ex of left apiiendix 

 auricuhe ; o, left ventricle. 



