. Text-book of embryology. Embryology. 554 EMBRYOLOGY OF THE LOWER VERTEBRATES oh. tubular communication between nose and mouth. The lachrymal groove is no longer visible: the lachrymal glands are developing as solid ingrowths of ectoderm. The pituitary body now forms a rounded mass of branched glandular tubes lying between the trabeculae and communicating with the buccal cavity by a narrow tubular duct opening immediately over the glottis. The air-sac rudiments make their appearance on the surface of the lung (Fig. 246, C, ). _ The mesonephric tubules have been growing actively up till now
. Text-book of embryology. Embryology. 554 EMBRYOLOGY OF THE LOWER VERTEBRATES oh. tubular communication between nose and mouth. The lachrymal groove is no longer visible: the lachrymal glands are developing as solid ingrowths of ectoderm. The pituitary body now forms a rounded mass of branched glandular tubes lying between the trabeculae and communicating with the buccal cavity by a narrow tubular duct opening immediately over the glottis. The air-sac rudiments make their appearance on the surface of the lung (Fig. 246, C, ). _ The mesonephric tubules have been growing actively up till now: the metanephric units are making their ap- pearance : the Muller- ian duct reaches the cloaca if it has not already done so although no actual communication is es- tablished until about six months after hatching. Ossification be- comes conspicuous in the limb - bones and the investing bones of the head. The keel of the sternum forms an ossification distinct from the two lateral rudiments of the body of the sternum. The terminal sinus of the vascular area has disappeared. The septum of the conus is now completely traversed by muscle so that both aortic and pulmonary cavi- ties are completely ensheathed by muscle. The splitting apart of the two vessels is inaugurated by the appearance of a longitudinal incision along the line of attachment of the septum. As regards the further progress of development the following approximate times may be mentioned. About the ninth day the oesophagus gradually becomes patent again. On the tenth day the arterial arches have practically assumed the definitive condition and the metapodial skeleton is Fig. -Chick extracted from egg during seventh day showing operculum {op).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original MacBride, E. W. (Ernest William), 1866-1
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Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
