The development of the caeca in the chick embryo. Morphometric and morphological remarks.

Quantitative aspects of the organogenesis of the chick embryo caecum (proximal and distal tracts) were investigated from the 8th to the 15th day of incubation. Histological sections were studied by means of a computerized morphometric system and a semiautomatic digital system (Videoplan 2). The total area of sections, of the lumen, the caecal wall and its components (subserous stratum, muscle layer, lamina propria, epithelium) and the thickness of the epithelium and muscle layer were measured. The mean +/- S.E.M. of the obtained values was calculated. The percentage of shrinkage, due to histological procedures, was calculated for each day considered. The mean values for each day of incubation were modified on the basis of the shrinkage percentage. The differences between the mean values of the areas of the proximal and distal tract were statistically evaluated. Exponential curves and the r coefficient were determined in order to evaluate the general growing pattern of the mean area of the caecal wall components as a function of age. The obtained results demonstrate that there are some differences between the proximal and distal tract of the caecal anlage in the growth pattern of the wall components. In the proximal caecal tract, the lamina propria showed the highest growth rate, while in the distal tract, the caecal wall component the subserous stratum did. Moreover, the caecal anlage showed different developmental behaviour from the ileum, duodenum and colon in the same chick embryo.