No. 2.] EMBRYOLOGY OF THE LIZARD. T^iy 



lo, A, the ventrally curved part of the notochord is visible (iV", 

 Fig. II, A). Its anterior end fuses with a mass of cells {HC) 

 which lie close to the ventral surface of the rudiment of the fore- 

 brain. In the fourth section, behind il, A, this mass of cells 

 {HC) is seen to be fused with the epiblast (Fig. 12, A). This 

 fusion with the epiblast is, however, continuous from side to 

 side across the median line. Five sections behind I2, A, this 

 mass of cells (^HC) is seen to be also completely fused with the 

 wall of the intestine {AL, Fig. 13, A). The section 13, A, 

 passes near the inner surface of the epiblast at Hph. The epi- 

 blast near this point lies close against the base of the anterior 

 medullary fold, AF. The epiblast at Hph is the roof of the 

 hypophysis, which, appearing at this early stage, remains per- 

 manently unmoved from this point of contact with the fore-brain. 

 Six sections farther backward, Fig. 14, A, represents a section 

 passing near the external surface of the roof of the hypophysis 

 (Hph), and cutting in its own plane the epiblast {Ep) which 

 covers externally the anterior medullary fold. Five sections be- 

 hind 14, A, the section 1 5, A, passes through the anterior curved 

 end of the amnion cavity (M.m). The wall of fused epiblast and 

 hypoblast, which separates the lumen of the intestine from the 

 amnion cavity, shows here its thinnest point in the median line, 

 and indicates where the mouth-opening will appear. Just pos- 

 terior to this point the epiblast recurves around over the head to 

 form the amnion, so that within five sections backward there is 

 no epiblast on the ventral side of the body. 



This manner of development of the notochord and hypo- 

 physis seems to point to some peculiar relation between the two 

 organs. There are also other parts which are intimately related 

 to these organs, namely, the muscular elements of the head, — 

 primarily the head-cavities, which are developed from the mass 

 of cells, HC. 



The next older embryo which I have been able to examine 

 is represented in the series of transverse sections, B. The 

 mouth-opening has not yet appeared. The notochord in the 

 head still lies close to the hypoblast, but the increased growth 

 of the brain has lifted the mid-brain away from the notochord. 

 In Fig. 19, B, is seen the ventrally curved portion of the noto- 

 chord {N). In 20, B, — four sections farther backward, — is 

 seen the dorsal wall of the intestine and its lumen {AL). 



