| Abstract: | The authors have investigated the morphological aspects of the wall components of the developing colon in the chick embryo (Gallus domesticus) from the 7th to th 15th day of incubation. Particular attention has been given to the lumen recanalization, phenomenon which occurs also in other animal species. The most significant results can be summarized as follows: 1) the lumen is recanalized at the 7th day only at the proximal part of the colon (Fig. 1, Tav. 1), while at the distal tract it is still completely filled by an epithelial plug (Fig. 2, Tav. 1). Therefore the recanalization of the lumen takes place cranio-caudad. 2) At the 8th day the process of recanalization of the lumen shows, in the distal part of the colon, well defined modalities. Radially oriented intraepithelial spaces within the epithelium filling the lumen join other semilunar intercellular spaces, which are placed near the central part of the occluded lumen (Fig. 3). By the junction of a couple of radially oriented spaces with one semilunar space, an U-shaped intercellular space derives, which delimits an incoming epithelial fold (Tav. 3). Such a phenomenon is continued also during the 9th and 10th day of incubation (Fig. 6, Tav. 2). 3) At the 11th day the colonic lumen is completely open and, in its distal part, the appearance of the primordial previllous ridges can be observed (Fig. 7). In the proximal tract the previllous ridges develop one day later (Fig. 8). 4) At the 13th day, in the distal part of the colon, the first appearance of crypts occurs (Fig. 10). So, while the process of recanalization of the lumen is cranio-caudad, the formation of previllous ridges and crypts proceeds caudo-cranially. 5) From the 11th day onwards the lamina propria is actively involved in the process of formation of the previllous ridges. Only at the 14th day, in the distal part of the colon anlage, the appearance of the muscularis mucosae is observed (Fig. 11). 6) The muscle layer and the subserous stratum do not show appreciable morphological changes in the course the considered period of incubation. |
