Gebäude 21, 1. OG
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In the mice outbred strain Han:NMRI the relationship between fetal weight and number of ossification centers of some skeletal districts an day 18 p.c. was analyzed. For this purpose 1725 fetuses were divided into eight weight classes. The average rate of ossification was calculated. It was checked if there was a sex and side (uterus horn) difference in fetal weight and extent of ossification. These data were used as a contribution to a general biological characterization of this strain. The following results were obtained:Relationship between fetal weight and extent of ossification1. The ossification of metacarpi, metatarsi and sternebrae was nearly complete and largely independent of fetal weight. 2. The ossification of the paws of hand and foot is complete in fetuses weighing more than 1.0 g and 1.1 g respectively. In fetuses with a lower weight there was a linear relationship between these two parameters. A similar correlation was found for neck vertebrae (weight limit = 1.2 g).3. The ossification of phalanges (hand and foot) as well as of tail vertebrae was incomplete and varied depending on the fetal weight.a) The relationship between fetal weight and the extent of ossification of foot phalanges and tail vertebrae can be described by a linear regression.b) For phalanges at the forepaws a quadratic regression can be used to correlate extent of ossification with fetal weight.4. In fetuses having a weight of < 1.0 g (number of fetuses = 140) the number of ossified tail vertebrae correlated very well with body weight.From all the associations investigated the number of tail vertebrae showed the strongest linear relationship with fetal weight. The rate of ossification of tail vertebrae was found to be a useful variable when studying druginduced retardation effects.5. The relationship between low fetal weight (less than 1.0 g) and the extent of ossification can be described by one common factor with nearly equal loadings on the phalanges (hand and foot) and neck and tail vertebrae.Relationship between fetal weight and sex and uterus horn (right vs. left)Because of the large number of fetuses studied a slight, but significant difference between the mean weight of the female and male fetuses was found. The male fetuses were slighter heavier than the females.No correlation was found between fetal weight and uterus horn (right vs. left).Relationship between ossification and sex and uterus horn (right vs. left)In phalanges and fore- and hindpaws there were significant differences between the number of ossification centers of the female vs. male fetuses. The male fetuses showed an advanced ossification at the developmental stage studied. No correlation was found between ossification and uterus horn(right. vs. left).Some characteristics of NMRI mice on day 18 p.c.1. The ratio of female fetuses to male fetuses was 54 % to 46 %. 2. The number of implantations in the right horn was higher than in the left horn.3. The average litter size was 10.7.4. The fetal weight showed a normal distribiltion.5. The mean percentage of "runts" (body weight < 0.8 g) was 1.4 %. 6. 1.1 % of total fetuses showed an additional ossification center between sternebra 5 and 6.