PART 1. 



THE HEART AXD BLOOD-YE^ELS, 



I. THE HEART. 



The original arrangement of this section has been modified.) 



THE heart is situated in the middle line above the central portion 

 of the shoulder-girdle and 31. sternohyoideus, and below the 

 oesophagus ; the apex is directed backwards and lies between the 

 of the liver, the base i> directed forward^, and lies a short 

 distance behind the larynx. The heart is surrounded by the 

 pericardium. 



A. The Pericardium [is a 

 very thin membranous sac. 

 which completely encloses the 

 heart ; it is attached, at some S.' 

 distance, to the large vessels P'-~ 

 passing to and from the heart, 

 and has inserted into it some "--*- 

 fibres of the M. olUqiiu* al- TA. 

 dominis iniernu* (see page 70). 

 A fold of the pericardium 

 extends from the dorsal sur- 

 face to the truncus arteriosus, 

 and through it courses the 

 vena cardiaca. 



The pericardium is a con- 

 nective-tissue membrane, and 

 is lined on either side with 

 endothelium, which is in part 

 ciliated (Leydig); the endo- 

 thelium of the inner surface 

 is continued on to the heart 



i: 



The heart and blood-vessels, seen from the ventral 



surface ; after Howes. 

 AC. Left anterior caval vein. 

 '. Carotid arch. 

 LA. Left auricle. 

 f. Right pulmo-cntaneou? arch. 

 BA. Right auricle. 

 S'. Left systemic arch* 

 TA. Truncus arteriosus. 

 F. Ventricle. 



