192 CIRCULATORY SYSTEM. 



muscular fibres is uniform in its venous portion, but on the 

 sinus is arranged into the parallel fasciculi called the Musculi 

 Pectinati; a circular fasciculus surrounds the orifice of the de- 

 scending cava. In the left auricle, the stratum of muscular 

 fibres forms a uniform layer, arid is also thicker than on the 

 right side. These fasciculi commence on the pulmonary veins 

 and run transversely across the auricle, with the exception of 

 the more deeply seated, which are irregular, and crossed upon 

 each other. The septum of the auricles is also formed by a 

 muscular stratum. 



In the ventricles, the superficial fasciculi observe a spiral 

 course, and many of those belonging to the left ventricle may 

 be traced over the right; as the fibres are more deeply situated, 

 they become shorter and more interwoven. In the septum, 

 between the ventricles, the fibres of the two cavities are much 

 interlocked; but, with some trouble, may be partially separated. 

 The fibres of the columns earner are too irregular in their 

 course to admit even of a general description. It would appear, 

 however, that they are a continuation of the superficial spiral 

 fibres of the ventricles which penetrate into the interior of the 

 heart at its apex, and leave there a small foramen which is 

 closed only by the pericardium, externally, and the lining 

 membrane of the heart. M. Gerdy asserts, that all the fibres 

 of the heart arise from, and are inserted into, the tendinous 

 rings forming the ostia venosa and the orifices of the arteries; 

 having in the mean time traversed the course which is peculiar 

 to the several fasciculi, according to their being superficial, in 

 the middle or deep-seated.* 



All the cavities of the heart are lined by a serous membrane, 

 resembling that of the blood vessels. 



Of the Blood Vessels of the Heart. 



The Heart is furnished with both arteries and veins, which be- 

 long to its nutritious system. 



The arteries, called Coronary, arise, as observed, from the 



* For a very detailed exposition of the structure of the Heart, see Wolff Act. 

 Acad. Petrop. 1781; and Gerdy, Journal Complementaire du Diet, des Sc. Med. 

 vol. x. p. 97. 



