No. 2.] EMBRYOLOGY OF THE LIZARD. 369 



Plate xv. 



Figs. 40, C, 41, C, 42, C. — See explanation of Plate XIV. 



Figs. 43, C, 44, C, showing coelenteric zone (CZ) and anterior end of 

 the notochord {N). These sections are immediately consecutive. A., artery. 

 Epi., epithelial lining of hypophysial invagination (^HpJi). HC, head- 

 cavity. ivHC, wall of head-cavity. {Z. 2. D.) 



Fig. 45. — Frontal section through the brain of young embryo of Sphrero- 

 dactylus, parallel to the brain-axis anterior to the cranial flexure. (This 

 embryo is more advanced than that of series A.) The assymmetry is due to 

 the twist of the embryo. MF, medullary-folds. Mes, mesoblast. 3fB, 

 mid-brain. FB, fore-brain. Opv, optic vesicle, already pointing back- 

 ward, the wall of the same (, Op) lying immediately under the epiblast {Ep). 

 o. external opening of the primary first ventricle at the anterior end of the 

 neural axis. {Z. 4. A.) 



Fig. 46. — Part of section through the fore-brain and eye in the same plane 

 as Fig. 45. L, lens. Opv, optic ventricle. O.si, lumen of optic stalk. 

 wjPj5, wall of fore-brain. (Z. 2. A.) 



Fig. 47. — Sagittal section through the head of young embryo, imme- 

 diately to one side of the median sagittal plane. Ep, epiblast. t'n.FB, 

 infundibular region of fore-brain. 7/C, proximal end of head-cavity. UpA, 

 hypophysial invagination. NyP, hypoblast. E% lower jaw. M, mouth. 

 (Z. 4. A.) 



