298 



EMBRYOLOGY. 



A, B, d}. Somewhat earlier than this, namely, about the 

 fourteenth hour, the first rudiments of the embryo become 

 distinctly visible in the middle of the germinal area, in the 

 guise of a delicate white elongated streak, about a line and a 

 half in length ; it is designated nota primitiva the primitive 

 streak, and lies in the line of the long axis of the germinal 

 area, which itself lies in the transverse axis of the egg (fig. 325, a) . 

 Under the nota primitiva, the cumulus proligerus, deeply seated, 

 may still be seen very plainly glistening through (fig. 326, A, 



B, d). The nota primitiva rises slightly above the level of 

 the germinal area (fig. 326, b) ; it is thicker and blunter ante- 

 riorly, or towards that end which becomes the head of the 

 embryo, thinner, and tending to a point posteriorly. The nota 

 primitiva is probably the groundwork of the brain and spinal 

 cord. 



[ 484. The nota primitiva, an aggregate of dark granules 



in the first instance, becomes 

 more fluent by and by, and 

 presents itself as a layer of de- 

 licate, transparent masses, by 

 the side of which, between the 

 sixteenth and eighteenth hour, 

 a pair of new formations arise 

 symmetrically, near the mid- 

 dle line. These are the lami- 

 nce s. plicfB dorsal es the dor- 

 sal laminae, two cylindrical 

 rolls or enlargements, which 



B 



Fig. 326. Ideal sections of fig. 

 323 (after Bae'r, with slight varia- 

 tions). A, transverse section ; B, 

 longitudinal section ; a, vitelline 

 membrane, indicated by a finely 

 dotted line ; b, nota, or primitive 

 streak, with the serous layer of the 



arise parallel to the nota primi- 

 tiva, and form a couple of cris- 



tse, or ridges, one on either 

 . , ., 9~ 00 - - Q r>o 



, Slde , of lfc (% s - 327 and 32 f ' 



blastoderma, corresponding to the &, ), which diverge anteriorly 



area pellucida ; c, mucous layer of and posteriorly, being nearest 



the blastoderma, corresponding to about the middle of their 



the area vasculosa ; d, cumulus pro- len th an ^ sloping somewhat 



hgerus s. nucleus cicatncuke. .,, ^ 



from without inwards, or to- 

 ward? one another. The angles of the ridges are softly 

 rounded off; each ridge has the appearance of a clear broad 

 line, which is included within two darker lines. The germinal 



