526 ANATOMY OF VERTEBRATES. 



septum of the foetal auricles ; bounded above by the prominent 

 crescentic border, or ' annulus ovalis.' The opening into the 

 ventricle is bordered by a sclerous oval ring, to which muscular 

 fibres of both auricle and ventricle are attached ; the ring being 

 thicker for the latter. 



In the Human right ventricle the portion of the tricuspid valve 

 nearest the orifice of the pulmonary artery is the largest, and is 

 divided by deeper notches from the two smaller portions than 

 these are from each other: the chordae tendineae from each 

 columna carnea are inserted, generally into the contiguous borders 

 of two portions of the valve : the muscular prominences of the 

 inner surface of the ventricle have either their inner or central 

 surfaces free, or are free in the circumference of their middle part 

 but attached at both ends, like beams ( trabecular ), or they project 

 freely in a conical form, as ' columnar mammillares : ' they are 

 least developed in the conical prolongation of the cavity, (infundi- 

 bulum, conus arteriosus), from the apex of which the pulmonary 

 artery arises. The arterial orifice of the ventricle is formed by 



405 406 



Annulus arteriosus, with attached fibres of 



right ventricle, clxxxvii". Sigmoid valves, right ventricle, clxxxvi 



sclerous tissue, which a dissector may define as a ring, fig. 405, 

 disposed in three crescentic curves, with the convexities, a, a 9 

 toward the ventricle, and the blended horns, d, b, projecting 

 toward the artery : the ring is represented as cut through at one 

 of these points of confluence, e, e, in order to its being spread out. 

 Muscular fibres of the right ventricle, /, /, are attached to the 

 convexities of the ring ; the fibrous coat of the artery is attached 

 to the outer margin, the sigmoid valves, fig. 406, a, a, to the 

 inner margin, of the upper or arterial surface of the concavities 

 which owe their definition to the junction of the endocardium to 

 such valvular attachments. The right ventricle continues to show, 

 in Man as in other Mammals, the same relation, as an append- 

 age to the left, which is illustrated in the section of the Bird's 

 heart, vol. ii., fig. 92, forming, as so seen, a concave parabolic 

 section of a cone, applied to the more perfect cone of the left 



