Development of the Alimentary Canal
Outlines of the form and position of the alimentary canal in successive stages of its development. A, alimentary canal, in an embryo of four weeks; B, at six weeks; C, at eight weeks; D, at ten weeks; l, the primitive lungs connected with the pharynx; s, the stomach; d, duodenum; i, the small intestine; i’, the large intestine; c, the caecum and vermiform appendage; r, the rectum; cl, in A, the cloaca; a, in B, the anus distinct from s i, the sinus uro-genitalis; v, the yolk sac; vi, the vitellointestinal duct; u, the urinary bladder and urachus leading to the allantois; g, genital ducts.
Baker, W. Morrant & Harris, Vincent Dormer Kirkes' Hand-book of Physiology, 13th ed. (Philadelphia: P. Blakiston's Son & Co., 1892) 840