JOURNAL OF MICROSCOPICAL SCIENCE. 



DESCRIPTION OF PLATES II & III, 



Illustrating Dr. A. Milnes Marshall's Paper on the Develop- 

 ment of the Cranial Nerves in the Chick. 



All the figures were drawn with a Hartnack camera. The numbers 

 attached indicate the magnifying power, in diameters, employed in drawing 

 eacli figure. All the drawings are from single sections, except fig. 21, in 

 which two consecutive sections were employed. A large number of the 

 figures are semi diagrammatical, there being no object to be gained by 

 representing the mesoblast or the histological details ; the outlines are, 

 however, strictly accurate in all cases. 



ALPHABETICAL LIST OF REFERENCES. 



a, Point at which the secondary attachment of the nerve to the neural 

 canal occurs ; al., alimentary canal ; aor., dorsal aorta ; and., auditory 

 epithelium ; b, primary attachment of nerve to summit of neural canal ; 

 br.\, first branchial arch; br. 2, second brancliial arch; c./., choroidal 

 fissure; c. A., cerebral hemispheres ; cow., longitudinal nerve commissure; 

 ep., external epiblast ; y. ^., fore-brain ; y. y., fore-gut ;/!;». ^., constric- 

 tion between fore- and mid-brain ; A. b., hind-brain ; Hy., hyoid arch ; Ay., 

 hypoblast ; i/i/., iufundibulum ; i. v., investing mass ; /., lens ; n., neural 

 ridge; m. b., mid-brain; m. ff., mid-gut; m. h. b., constriction between 

 mid- and hind-braiu ; mn., mandibular arch ; m. p., muscle-plate ; mx., 

 maxillary process; «., notochord ; o. c, optic cup ; olf., olfactory pit; o. v., 

 optic vesicle ; pit., pituitary diverticulum ; p.v., prolovertebrae ; r. e., rec- 

 tus externus ; r. i., rectus internus ; r. s., rectus superior; sp., spinal 

 ganglion; v. c, visceral cleft; I — X, cranial nerves (Sommering) ; VI, 

 ophthalmic nerve ; V 2, superior maxillary nerve ; V 3, inferior maxillary 

 nerve. 



PLATE n. 



Fig. 1. — Transverse section through the mid-brain of a twenty. seven 

 hours' chick, X 90. Specimen hardened in ^ p. c. chromic acid, to which 

 a few drops of a 1 p. c. solution of osmic acid was added ; allowed to 

 remain twenty-four hours. 



Figs. 2-5. — Transverse sections through the brain of a twenty-four hours' 

 chick. Hardened in same manner as fig. 1. x 90. 



Fig. 2. — Through anterior part of fore-brain ; two halves quite 



separate; no mesoblast. 

 Fig. 3. — Through posterior part of optic vesicles. The section is 

 imperfect, especially at its lower part, where the roof only of the 

 fore-gut is present. 

 Fig. 4. — Through widest part of mid-brain ; also imperfect. 

 Fig. 5.— Through hind-brain. 

 Figs. G-10. — Transverse sections through brain of a twenty-nine hours 

 chick. Specimen hardened in picric acid for three hours. X 90. 

 Fig. 6. — Tliroiigh anterior part of optic vesicles. 

 Fig. 7. — Through constriction sepamting fore- and mid-bruii.s. 

 Fig. 8. — Through middle of mid-brain. 



