20 C. W. M. Poynter 



septum is present in about 36 per cent, of all cases of heart 

 anomalies. As shown by the number of cases living to an ad- 

 vanced age the disturbance to the circulation, even from a com- 

 plete absence of the septum, is readily compensated. 



B. INTERATRIAL SEPTUM 



I. Atrial Septum Absent 



In these cases the growth disturbance has inhibited the devel- 

 opment of both the septum primum and secundum. I have not 

 found the condition as an isolated anomaly, but it is frequently 

 found in conjunction with absence of the interventricular septum. 

 The condition constitutes 16 per cent, of atrial septum dis- 

 turbances. 



I. Atrial septum absent: Mery (1700), Wilson (1798), Ring (1805), 

 Standert (1805), Farre (1814), Otto (1814), Meckel (1815), Marx (1820), 

 Cheever (1821), Martin (1826) 2 cases, Cerutti (1827), Mauran (1827), 

 Mayer (1827), Thore (1842) (1845), Crisp (1846), Foster (1846), Rams- 

 botham (1846), Foster (1847), Darrach (1857), Clar (1858), Bernard 

 (i860), Guibert (i860), Almagro (i860), Cameron (1871), Maier (1876), 

 Marchand (1881), Robinson (1881), Shattock (1883), Jacoby (1884), Bull 

 (1885), Northrup (1888), Chapatot (1889), Birmingham (1892), Probyn- 

 Williams (1894), Cade (1897), Ewald (1898), Hunsberger (1898), Rudlof 

 (1900), Blondel (1901), Griffith (1902), Champeter (1903), Lefas (1904), 

 Chartier (1905), Bernstein (1906), Konstantinowitsch (1906), McCrae 

 (1906), Carpenter (1908), Girauld et Tissier (1910), Metzger (1911), 

 Knope (1912). 



2. Anomalies of the Septum Primum 



In these cases two different conditions must be recognized. 

 When the defect is along the dorsal (venous) wall Ingalls (1907) 

 has pointed out that it seems to be due to development of the 

 septum primum too far to the right, so that instead of passing 

 to the left of the opening of the superior vena cava it passes di- 

 rectly through it and so creates an opening. When the opening 

 is in the lower part of the septum, above the ventricles, it may 

 be explained as a persistence of the ostium primum either through 

 arrest of development of the septum primum or of the endocar- 

 dial cushions. The latter cases are characterized by a semi- 

 lunar opening low down in the septum. 



