532 



BLOOD-YASCULAR SYSTEM OF THE HORSE 



at the summit of the conus arteriosus, opposite to the lower part of the third 

 intercostal space. It is guarded by the pulmonary valve, composed of three semi- 

 lunar cusps (Valvulse semilunares arterise pulmonalis) ; of these, one is internal, one 

 external, and the third posterior. The convex peripheral border of each cusp is 

 attached to the fibrous ring at the junction of the pulmonary artery and the conus 

 arteriosus. The central border is free and slightly concave. Each cusp consists 

 of a layer of endocardium on its ventricular surface, a continuation of the inner coat 

 of the artery on its arterial surface, and an intermediate layer of fibrous tissue. 

 The upper edge of the conus arteriosus forms three arches with intermediate 

 projecting angles or horns, to all of which the cusps are attached; and the 



Musculi pectinati 



Pahnoimnj (irfcr;/ 



Musculi ^. 

 pectinati \^^^'-' 



Aortic valve --i-K-- - 



Great coronary 

 vein. 

 Left coroniiry , 



artery 

 Bicuspid valve' 



CliordcF tcndincm 

 Papillary muscle 



■-,--- Right coronary 

 artery 



f^~~ Tricuspid valve 



^i.^^ Papillary 

 muscle 



Traheculce 

 carnece 



Fig. 424. — Section op Heart of Horse. Specimen H.\rdened hi situ. 

 The section is cut nearly at right angles to the ventricular .septum, and is viewed from the right and posteriorly. 



artery forms opposite each cusp a pouch, the sinus of the pulmonary artery (or 

 of Valsalva). 



The walls of the ventricle (except in the conus arteriosus) bear muscular ridges 

 and bands, termed trabeculae carneae. These are of three kinds, viz., (1) ridges or 

 columns in relief; (2) musculi papillares, somewhat conical flattened projections, 

 continuous at the base with the wall and giving off the chordae tendinea; to the 

 tricuspid valve; (3) moderator bands (Musculi transversi cordis) which extend 

 from the septum to the opposite wall. The latter are partly muscular, partly 

 tendinous, and vary in different subjects. The strongest one is usually about 

 midway between the base and apex and extends from the septum to the base of 

 the anterior musculus papillaris. It is considered that they tend to prevent 

 overdistention. 



