. The development of the chick; an introduction to embryology. Birds -- Embryology. fro:m twelve to thirty-six somites 169 apex, so that by the stage of 29 somites the opening is reduced to a minute ellipse situated on the external side of the dorsalmost portion of the otocyst (see Fig. 93). This portion of the otocyst now begins to form a small conical elevation, and the final closure takes place on the external side of this elevation, which is destined to form the endolymphatic duct. The latter remains united to the epi- deTmis at this point for a consid- erable period of time by a s
. The development of the chick; an introduction to embryology. Birds -- Embryology. fro:m twelve to thirty-six somites 169 apex, so that by the stage of 29 somites the opening is reduced to a minute ellipse situated on the external side of the dorsalmost portion of the otocyst (see Fig. 93). This portion of the otocyst now begins to form a small conical elevation, and the final closure takes place on the external side of this elevation, which is destined to form the endolymphatic duct. The latter remains united to the epi- deTmis at this point for a consid- erable period of time by a strand of cells which may preserve a lumen up to 104 hours (Fig. 98). The final point of closure of the oto- cyst is thug very definitely placed, and it coincides with the middle of the endolymphatic duct, that is, with the junction of the later formed saccus and ductus endolymphaticus. In the Selachia this duct remains in open communication with the exterior throughout life; the rela- tively long persistence of its con- nection with the epidermis in the chick may thus be interpreted as a phylogenic reminiscence of the an- cestral condition. The Nose (Olfactory Pits). At about the 28 s stage, the ectoderm on the sides of the head a short dis- tance in front of the eyes appears thickened. Two circular patches of the surface to the otocyst. D. ectoderm are thus marked off, the end'l. Endolymphatic duct D, . . Dorsal. Ect., Ectoderm of the begmnmg of the olfactory epithe- surface of the head. Gn., Audi- Hum; at first this grades almost im- tory ganglion. L., Lateral. M., ... - .... Median, v., ventral, perceptibly nito the neighboring ectoderm. In the stages immediately following the olfactory plates appear to sink down towards the ventral surface of the head, due no doubt to more rapid growth of the dorsal portion of the head. Thus they appear at the ventro-lateral angles of V. iWin^P Fig. 98. — Section of the otocyst of an embryo of 104 hours. The original opening of the otocys
Size: 1185px × 2107px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrattray187, bookcentury1900, bookdecade1900
