906 



EMBRYOLOGY. 



from the vertebral laminae; in the cephalic region they always remain 

 adherent to them, and at this point they are named the cephalic lamince. 



1. The proper lateral lamince are divided into two layers : an external and 

 an internal, united by the middle lamina, and including between them a 

 cavity which becomes that of the pleura and peritoneum the pleuro- 

 peritoneal cavity. It is after these primary modifications that the lateral 

 laminae are fused to the vertebral laminae. 



The internal lamina, also named the fibro-intestinal lamina, envelops the 

 deep portion of the blastodermic layer or intestinal furrow, the umbilical 

 vesicle, and the allantois. It constitutes the fibrous and vascular part of 

 these membranes, and carries the vessels to the inner face of the chorion. 



The external or cutaneous lamina is developed in two directions. Above, 

 it passes between the muscular laminae and the foetal portion of the external 

 layer of the blastoderm, to form the skin of the back. Below, it separates into 

 two other laminae, which receive between them the prolongations of the 

 muscular laminae, destined to the formation of the intercostal and abdominal 

 muscles and the ribs. Of these two secondary laminae, the external forms 

 the skin of the trunk, and the internal the parietal layer of the peritoneum. 



The cutaneous laminae also have an extra-foetal prolongation the fibrous 

 layer of the amnion. 



Fig. 433. 



THE EARLY" STAGES OF THE DEVELOPMENT OF THE BODY OF A FOWL. 



A, The first rudiment of the embryo ; a, Its cephalic, and b, its caudal end ; c, The 

 primitive groove. B, The embryo further advanced ; a, 6, c, As before ; d, The 

 dorsal laminae as yet developed only in the cephalic region, and not quite united 

 in the middle line ; e, The protovertebrae. c, The letters as before. The dorsal 

 laminae have united throughout the greater part of the cephalic region, and are 

 beginning to unite in the anterior spinal region. D, Embryo further advanced, 

 the dorsal laminae having united throughout nearly their whole length; the 

 protovertebras have increased in number, and the omphalo-mesenteric veins, /, 

 are visible. 



With regard to the middle or mesenteric lamina 1 , they are confounded in 

 the mesial line, and in their texture are developed the Wolffian bodies and 

 the principal vessels of the trunk. 



