98 RUDIMENTARY SPINA BIFIDA. 



condition of delayed development which has been present throughout the spine 

 at an earlier period. 



The bony closure of the posterior vertebral arches begins in the lumbar region, 

 proceeding upward and downward from this point. In a model of the chondro, 

 cranium and cervical vertebrae of a 42 mm. embryo (No. 886, Carnegie Collection) 

 made by Dr. C. C. Macklin, the cartilaginous closure of the atlantal neural arches 

 lags considerably behind that of the other cervical vertebrae, which evidence also sub- 

 stantiates this sequence in the cervical region. As is the case with other growth 

 phenomena, there must be considerable variation in the time of completion of this 

 process. According to Hennig (1880) the lumbar spinous processes are ossified by 

 the third year. Macalister (1893) gives time of completion of the dorsal arch in 

 the atlas as the fourth year, and Radlauer (1908) states that ossification of the 

 sacral spinous processes, beginning with Si in the third year, is finally completed 

 with S 4 and S 5 in the seventh year. 



Incomplete closure of the sacrum has been the subject of numerous studies. 

 In 1902 W. R. Smith noted the variation associated with left-sided sacralization of 

 the fifth lumbar in a female Australian aboriginal sacrum, and more recently Rad- 

 lauer (1908), Adolphi (1911), Frets (1914), and Wetzel (1915) have contributed 

 considerable data on the subject. Radlauer studied 500 sacra, representing various 

 races, from the University of Zurich and from several German collections. He 

 found a completely open sacral canal in 5 per cent of the cases. He found also that 

 closure of the hiatus sacralis occurred more frequently, (1) over the fourth and 

 between the fourth and fifth sacral vertebra, 45.6 per cent; (2) over the third and 

 between the third and fourth sacral vertebra, 27.4 per cent; and (3) over the fifth 

 sacral vertebra, 14 per cent. 



Adolphi (1911), working in Dorpat with 292 skeletons (234 male and 58 

 female), found an open sacral canal in 3.4 per cent of the males and 1.7 per cent of 

 the females a total of 3.08 per cent. 1 In 50.3 per cent (48.7 per cent of males and 

 56.9 per cent of females) there were 4 sacral vertebrae closed; 2 in 24.3 per cent (25.2 

 per cent of males and 20.7 per cent of females) 3 vertebrae were closed; 3 while in 

 12 per cent of both males and females 5 vertebrae were closed. 4 In 12.7 per cent 

 there was some degree of opening of the first sacral arch. 5 In a group of 203 speci- 

 mens (161 male and 42 female), in which there were 5 and 6 vertebrae with no 

 transitionally formed ones, he found that the hiatus sacralis reached to the third 

 vertebra 6 in 26.6 per cent (28 per cent of the males and 21.4 per cent of the females) ; 

 to the fourth vertebra 7 in 51.2 per cent (48.4 per cent of males and 61.9 per cent of 

 females); and to the fifth vertebra 8 in 12.3 per cent (13 per cent of males and 9.5 

 per cent of females) . 



Frets, in material drawn from the population of Amsterdam, in which no 

 Jewish skeletons were included, found that out of 750 specimens the sacral canal 



'Adolphi's table 4. 4 Adolphi's table 3, column 1. 'Adolphi's table 5, columns 2 and 6. 



2 Adolphi's table 3, columns 2 and 5. 6 Adolphi's table 4, column 2. 'Adolphi's table 5, columns 1 and 5. 



3 Adolphi's table 3, columns 3 and 6. 'Adolphi's table 5, columns 7 and 9. 



