. Text-book of embryology. Embryology. FOWL—THIRD DAY 541 cular cavity while upon each side and ventrally1 there is seen a localized thickening (olf) of the ectoderm: this is the dimple-like rudiment of the olfactory organ. To return to the main part of the section—there is seen in its centre the wide pharyngeal space and on the embryo's left side the pharyngeal wall pro- jects out to the ectoderm as an endodermal pocket—the rudiment of the second visceral cleft (). Immediately ventral to the pharynx is the ventral aorta (). On the left side of the embryo the aortic root () is see
. Text-book of embryology. Embryology. FOWL—THIRD DAY 541 cular cavity while upon each side and ventrally1 there is seen a localized thickening (olf) of the ectoderm: this is the dimple-like rudiment of the olfactory organ. To return to the main part of the section—there is seen in its centre the wide pharyngeal space and on the embryo's left side the pharyngeal wall pro- jects out to the ectoderm as an endodermal pocket—the rudiment of the second visceral cleft (). Immediately ventral to the pharynx is the ventral aorta (). On the left side of the embryo the aortic root () is seen immediately dorsal to the pharynx, while on the right side—the section not being accurately transverse— a hoop-like aortic arch () is seen passing dorsalwards round the side of the pharynx from ventral aorta to aortic root. The large. Fig. 237e. -Transverse section passing through the second visceral cleft and the olfactory rudiment. , third aortic arch: , anterior cardinal vein; am, amnion; , aortic root; , false amnion; , forebrain; , hind brain; olf, olfactory rudiment; ph, pharynx; , ventral aorta; , second visceral cleft. vessel lying dorsal and slightly external to the aortic root () is the anterior cardinal vein. Traced tailwards it is found to open into the dorsal end of the duct of Cuvier. The neural tube () is seen to have a thin roof and widely expanded lumen indicating that it is now passing into the region of the hind brain. In tracing the series of sections further forwards it will be realized that the front part of the head region is, owing to its reflexed position, actually being traced in a morphologically tailward direction. In the section figured (Fig. 237f) the reflexed portion of the head is cut at the level of the eye rudiments (opt) which are seen to be in the optic cup stage with the inner or retinal layer 1 It will be realized from an inspection of the figure of the entire embryo tha
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Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
