THE OIRCTLATIOX. 



227 



cilia r fiber found chiefly in the vicinity of the foramen ovale and 

 in the valve of Yieussens; (2) those having a syncytial arrangement 

 found for the most part in relation to the superior vena cava and 

 the parts related thereto; (3) those of a reticular structure of the 

 sino-auricular node (Keith and Flack), and the tissue encircling the 

 greater part of the superior circumference of the superior-vena cava 



n 



Fig. 66. Course of Muscular Fibers of Heart. (LANDOIS.) 



I. Course of the musculai fibers on the left auricle, with the outer trans- 

 verse and inner longitudinal fibers, the circular fibers on the pulmonary veins 

 (v. p.). V, The left ventricle. (JOHN REID.) 



II. Arrangement of the striped muscular fibers on the superior vena cava. 

 c, Opening of the vena azygos. T 7 , Auricle. (ELISCHER.) 



and the valve of Yieussens. Gibson supposes the syncytial fibers 

 may originate the heart-beat. 



Pericardium. This is a fibro-serous sac inclosing the heart, and 

 consists of two leaves, or layers. The internal serous, .or visceral, 

 layer closely invests the heart and the commencement of the great 

 blood-vessels. It is an inextensible membrane. 



