ARREST OF DEVELOPMENT. 89 



386. A small Human heart, with a semilunar opening at the 



upper part of the ventricular septum. The pulmonary 

 artery has not half its normal calibre. The left auricle 

 and the left auricular ventricular opening are much con- 

 tracted. The mitral valves are very imperfect. The 

 right auricle is enormously dilated, its walls being en- 

 tirely membranous in places. 



The condition of the pulmonary artery and the dilated 

 right auricle point to an imperfect condition of the lungs, 

 with corresponding venous congestion. Unfortunately 

 no history has been preserved. 



387. A Human foetal heart, with the position of its great vessels 



reversed (situs mutatus) . There is no trace of a ventri- 

 cular septum. There is but one auriculo-ventricular 

 opening, with five valves around its margin. There is 

 one large auricle with a small pouch on its right side ; 

 this pouch has an auricular appendix, and obviously re- 

 presents the systemic auricle. The larger left auricle is 

 pulmonary ; but it also receives the superior and inferior 

 cava. 



d. Of an artery (stenosis). 



Is usually accompanied by other abnormal conditions. See 

 No. 386, where there is partial stenosis of the pulmonary 

 artery. 



e. Premature closure of the ductus arteriosus or foramen ovale. 

 This sometimes occurs. It may either be looked upon, like 

 stenosis of the arteries, as a form of arrest, or it may result from 

 disease or from some other malformation. 



f. Of a valve. 



Occasionally one of the flaps of the arterial or auriculo- 

 ventricular valve is arrested and remains rudimentary. This 

 condition is usually accompanied by disease of the valves, warty 

 growths on the endocardium, or even pericarditis. It is pro- 

 bably the result of congenital disease. 



388. A portion of the heart of a Boy ten years of age with two 



of the aortic valve-flaps united into a single flap. The 



