Archive image from page 150 of The development of the chick;. The development of the chick; an introduction to embryology . developmentofchi00lill Year: 1908 FRO:\r TWELVE TO THIRTY-SIX SOMITES 131 chapter. The lateral limiting sulci are a continuation of the lateral limbs of the head-fold; they owe their origin to the folding of the splanchnopleure and somatopleure adjacent to the embryo towards the yolk, at the line of junction of embryonic and extra- embryonic parts. The tail-fold arises about the stage of 26 to 27 somites (Fig. 93), and is similar to the head-fold, except that it is turne
Archive image from page 150 of The development of the chick;. The development of the chick; an introduction to embryology . developmentofchi00lill Year: 1908 FRO:\r TWELVE TO THIRTY-SIX SOMITES 131 chapter. The lateral limiting sulci are a continuation of the lateral limbs of the head-fold; they owe their origin to the folding of the splanchnopleure and somatopleure adjacent to the embryo towards the yolk, at the line of junction of embryonic and extra- embryonic parts. The tail-fold arises about the stage of 26 to 27 somites (Fig. 93), and is similar to the head-fold, except that it is turned in the opposite direction. The sulci combine to form a continuous ring around the embryo and gradually pinch it off, so to speak, from the extra-embryonic blastoderm. In the splanchnopleure the limiting sulci (Fig. 69) come to- Mesacsrd 'o/- Fig. 69. — Transverse section through the fifth somite of the 23 s stage. Amn., Amnion. Ao., Aorta, a. i. p., Anterior intestinal portal. Coel., Coelome. Chor., Chorion. Ectam., Ectamnion. E. E. B. C, Extra-embry- onic body-cavity. Int., Intestine. 1. 1. s., Lateral limiting sulcus. My., Myotome, s. a., Segmental artery. So'pi., Somatopleure. Spl'pl., Splanch- nopleure. Somite, s. 5, Fifth somite. V. O. M. R. and L., Right and left omphalo-mesenteric veins. V. V., Vitelline vein. gether and fuse both in a caudal direction from the fore-gut, and subsequently in a cephalic direction from the hind-gut (see below), so as to convert the splanchnic gutter into a tube (the alimentary canal). There is thus a ventral suture along the alimentary canal in which the entoderm of the alimentary canal becomes separated from the extra-embryonic entoderm, thus leaving a double layer of the splanchnic mesoblast (ventral mesentery) connecting the alimentary canal with the extra-embryonic splanch- nopleure; but this disappears everywhere as soon as formed, except in the region of the posterior part of the heart and the liver where it forms th
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