588 CIRCULATORY APPARATUS. 



It offers hvo ivalls, an apex, and a base. 



Walls. — The anterior waU is concave ; its thickness is more considerable 

 above than below, and averages ^^ of an inch. The posterior ivall is convex, and 

 formed by the septum ventriculorum. 



Both walls are uneven, from the presence of fleshy columns (columnce carnece), 

 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 {musculi papiJlares) — thick and short, and fixed by their 

 base to the walls of the ventricles — have a free summit, into which are implanted 

 the tendinous cords {chordce tendincB) proceeding from the auriculo-ventricular 

 valve ; those of the second order (trabeculce carnce) are free in their middle part, 

 and attached by their extremities to the walls of the heart ; while the third 

 description {columned) adhere throughout their length to the cardiac tissue, on 

 which they stand as if sculptured in relief. 



In the right ventricle, two columns of the first order, rarely three, are met 

 with — one on the anterior, the other on the posterior wall. The columns of the 

 second order number two or three principal ones, extending from one wall to the 

 other, or attached to two different points of the same wall. There also exist a 

 considerable number of small ones intermixed with those of the third order. 

 The latter are particularly abundant in the angles formed by the union of 

 the two faces, where they interlace and give rise to more or less complicated 

 areolae. 



Apex. — The cipex of the right ventricle does not descend to the point of the 

 heart, being distant from it about H inches. 



Base. — This has two large orifices — the auriculo-ventricular and the pidmonary 

 openings. 



Auriculo-ventricular optening. — Placed on a level with the constriction that 

 divides the right heart into two superposed compartments, this orifice — widely 

 open and almost a regular circle in outline — forms the communication between 

 the auricle and ventricle. It is provided with a valvular fold that exactly closes 

 the orifice when the ventricle contracts to propel the blood into the lungs, and 

 which is termed the tricuspid (having three points) valve, in consequence of 

 its form. This valve offers : 1. A superior border, attached to the entire margin 

 of the auriculo-ventricular opening. 2. An inferior opening, free, cut into three 

 festoons by three deep notches, and fi-xed to the ventricular walls, principally 

 on the summits of the fleshy columns, by means of the tendinous cords which 

 ramify on reaching the valve. One of these festoons— more developed than the 

 others — is placed on the limit of the auriculo-ventricular and pulmonary 

 openings ; thereby constituting a kind of vertical partition that divides the 

 ventricular cavity at its base into two compartments — a right or auricular, and 

 a left or arterial. The other festoons are apphed to the anterior and posterior 

 walls of the ventricle. 3. An external face, which receives the insertion of a 

 great number of tendinous cords, 4. An internal face, which becomes superior 

 when the valve is raised to close the opening, when it constitutes the floor of the 

 auricular cavity. 



Pulmonary opening. — This orifice represents the entrance of the pulmonary 

 artery. Situated in front and to the left of the preceding, but a little higher, it 

 occupies the summit of a kind of infundibulum (the conus arteriosus) formed by 

 the left compartment of the ventricle being prolonged upwards. It is perfectly 

 circular, smaller than the artery to which it gives origin, as well as the auriculo- 



