24 C. W. M. Poynter 



cially to the cases of dilation. Cases of congenital dilation 

 and contracture have been reported and it is possible that a cham- 

 ber may over or under develop, due to factors interfering with 

 growth ; however, it seems hardly worth while to burden this 

 study with a group of borderline cases. 



2. Accessory Septa in the Right Atrium 



This consists of a network or delicate membrane originating 

 from the region of the Eustachian or Thebesian valve and ex- 

 tending across the atrium to attach to some point on the septum. 

 Chiari (1897) explained the condition as the mal-development 

 of the valvula venosa sinistra or septum spurium. He was de- 

 scribing particularly the network ; a number of observers have 

 since called a similar structure the " Chiari Net or Netz." Other 

 cases characterized by a definite band, Ruge (1891) thought may 

 be a redundant septum primum. 



Monet (1833), Thompson (1843), Eskridge (1881), Geffrier (1881), 

 Moore (1882), Cayla (1884), Leo (1886), Ruge (1891), Lepine (1894), 

 Chiari (1897), Swan (1898), Le Count (1901), Ebbinghaus (1904), Lesieur 

 et Froment (191 1). 



B. ABNORMALITIES OF THE LEFT ATRIUM 



I. Contraction and Dilation 



The left atrium has been the seat of a congenital contraction 

 or arrest of development in cases observed by Peacock (1866), 

 Roach (1880), Packard (1896), and Lamouroux (1899). 



I have found no cases in which a dilation suggesting congenital 

 origin has been described. 



2. Accessory Septa in the Left Atrium 



This condition does not seem to have been recognized by the 

 earlier observers. The accessory septum stretches across the 

 atrium dividing off a right posterior superior chamber into which 

 the pulmonary veins open. Borst (1906) considers this septum 

 to be a misplaced septum primum; Griffith (1903a) concludes 

 that the band is a redundancy of the tissue of the valve of the 



