The trabeculæ carneæ (columnœ carneœ) are rounded or irregular muscular columns which project from the whole of the inner surface of the ventricle, with the exception of the conus arteriosus.
They are of three kinds: some are attached along their entire length on one side and merely form prominent ridges, others are fixed at their extremities but free in the middle, while a third set (musculi papillares) are continuous by their bases with the wall of the ventricle, while their apices give origin to the chordæ tendineæ which pass to be attached to the segments of the tricuspid valve.
There are two papillary muscles, anterior and posterior: of these, the anterior is the larger, and its chordæ tendineæ are connected with the anterior and posterior cusps of the valve: the posterior papillary muscle sometimes consists of two or three parts; its chordæ tendineæ are connected with the posterior and medial cusps. In addition to these, some chordæ tendineæ spring directly from the ventricular septum, or from small papillary eminences on it, and pass to the anterior and medial cusps. A muscular band, well-marked in sheep and some other animals, frequently extends from the base of the anterior papillary muscle to the ventricular septum. From its attachments it may assist in preventing overdistension of the ventricle, and so has been named the moderator band (Septomarginal trabecula).