Gebäude 21, 1. OG
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In the mice strains DBA/2JHan, BALB/cJHan and C57 BL/6JHan the number of ossification centers of some skeletal districts was investigated an day 18 p. c. and ampared. The fetuses were divided into four weight classes. lt was" checked if there was a correlation between fetal weight and sex and the stage of ossification. Fur-thermore, a general embryological characterization was carried out, litter data were compiled and compared between the strains. The following results were obtained:Ossification:1) The metacarpals, metatarsals and the sternum were nearly completely ossified. The stage of ossification was mostly independent of the fetal weight.2) The metacarpal I was not ossified an day 18 p.c..3) The ossification of the ribs was complete. The majority of the BALB/cJHan fetuses had one or two supernumerary 14th ribs in the lumbar district.4) The number of ossified phalanges and caudal vertebrae increased with increasing fetal weight in the strains BALB/cJHan andC57 BL/6JHan. In contrast, the heavier fetuses of the DBA/2JHan strain showed a small decrease in the stage of ossification of the phalanges of the fore and hind paws. The number of ossified caudal vertebrae increased with increasing fetal weight.5) The differences between the strains were very distinct in the cervical vertebrae. In the BALB/cJHan strain the number of ossification centers increased with increasing fetal weight, while in the DBA/2JHan strain such a correlation was not found. In the C57 BL/6JHan strain only a few fetuses had ossified cervical vertebrae.6) No correlation was found between fetal sex and the stage of ossification.General embryological characterization and litter data:1) Particularly in the BAIB/cJHan strain the control of the vaginal plug as a sign of impregnation was an unreliable method.2) The majority of resorptions happened in an early stage of pregnancy.3) There was no significant difference between the mean weight of the fetuses in the left and right horn. There was also no significant difference between the mean weight of the male and female fetuses.4) In the C57 BL/6JHan strain fetal weight was significantly higher when compared to the other strains.5) The number of implantations in the right horn was higher than in the left one.