THE CIKCULATORY SYSTEM. 423 



Cysts of the visceral pericardium have been described. We have seen 

 a pedunculated cyst, containing about 6 c.c. of clear fluid, hanging into 

 the pericardial sac from its attachment near the pulmonary artery. The 

 origin of such cysts is obscure. 



The Heart. 



Malformations and Malpositions. 



MALFORMATIONS OF THE HEART. The malformations of the heart are -usually 

 closely associated with malformations of the aorta and pulmonary artery. They de- 

 pend on arrest of, or abnormal, development ; on endocarditis, myocarditip, thrombosis, 

 or mechanical causes. 



I. The common arterial trunk is only partially, or not at all, separated into aorta 

 and pulmonary artery. The divisions between the heart cavities are at the same time 



FIG. 231. REPTILIAN HEART. 

 Shows one auricle and one ventricle. 1 



defective, so that there may be one ventricle and no auricles ; one ventricle and one 

 auricle reptilian heart (Fig. 221) ; or one ventricle and two auricles. * 



II. The trunk of the pulmonary artery or of the aorta is stenosed or obliterated, and 

 from the obstruction to the current of blood there is interference with the development 

 of the septa between the heart cavities. 



1. The aorta, at its origin, or in the ascending portion of the arch, is stenosed or 

 closed. The pulmonary artery gives off the descending aorta, and supplies the carotids 

 and subclavians. The foramen ovale remains open, or there is no septum between the 



1 For a description of this case see Northrup, Trans. N. Y. Path. Soc., 1888, p. 41. 



