322 EMBRYOLOGY. 



outwardly from each mesenteric lamina, in the angle formed 

 between this and the ventral lamina in the line of the verte- 

 bral column, from the region of the heart as far as the allan- 

 tois. Even at this early period they exhibit interchanging 

 elevations and notches, and a canal or duct running in the 

 line of their long axis. On the fourth day the corpora Wolf- 

 fiana are recognized as being formed out of hollow co3cal-like 

 appendages, which are attached along the course of the duct 

 or canal (fig. 341, q, q, q, q) ; on the fifth day they look very 

 broad and thick, and the co3cal appendages are convoluted. 

 The germ-preparing sexual organs, the testicles and ovaria, 

 make their appearance as delicate striae on the inner sides of 

 the corpora Wolffiana. 



492. The metamorphoses of the mucous layer of the ger- 

 minal membrane begin, during this period, with the formation 

 of the intestinal canal. After the mucous layer, above the 

 involucrum capitis, has struck in under the head, and formed 

 the anterior access to the intestinal canal, fovea cardiaca, the 

 same layer also bends in at the opposite extremity, over the 

 involucrum caudse or caudal envelope, and here forms the 

 posterior access to the intestine, foveola inferior ; by the 

 increased curvature of the embryo, and the growth of the 

 ventral laminae, these depressions form funnel-shaped hollows, 

 which terminate, in blind extremities, towards the head and 

 tail. Almost simultaneously with the formation of the bran- 

 chial fissures, or perhaps a little earlier, the space between 

 the fore end of the head and the heart grows thin, and the 

 mouth and fauces break through, so that a free communica- 

 tion results betwixt the fovea cardiaca and the cavity of the 

 amnion (fig. 343, B, h). The intestinum rectum, on the 

 other hand (the posterior funnel-shaped involution of the 

 mucous layer), continues longer closed. By the formation of 

 the mesenteric laminae the rnucous layer is detached from the 

 ventral laminae, and pushed downwards (fig. 338, A, under e) ; 

 as soon as the mesenteric laminae have coalesced, the mucous 

 layer also converges from both sides under the mesentery, 

 and where it is accompanied by the prolongations of the vas- 

 cular lamina, which proceed from the mesenteric laminae, two 

 new laminae present themselves, the intestinal lamina, 

 laminae intestinales, which run perpendicularly downwards 



