THE EYE. 



391 



extend round its margin and cover the outer surface as well. 

 There are no veins which correspond exactly to this artery, the 



Fig. 156. — A transverse section across the head of a Babbit Embryo of the 

 twenty-first day, the section passing through the centres of the eyes {of. 

 Figs. 149 and 151). x 8. 



BE, orbit o-sphenoidal cartilage. BY, olfactory lobe. CC, cornea. DA, suborbital 

 gland. DB, submaxillary gland. DC, duct of submaxillary gland. DE, hair follicles. 

 ET, pre-sphenoidal cartilage. PA, frontal bone. HB, basihyal cartilage. MB, 

 mandible. MC, Meckel's cartilage. OB, buccal cavity. OC, inner or retinal layer of 

 optic cup. OD, outer or pigment layer of optic cup. OG, iris. OL, lens. OM, 

 upper eyelid. OO, lower eyelid. PP, posterior narial passage. PI, palatine bone. 

 TE, decidiious grinding tooth of upper jaw. TP, permanent grinding tooth of upper 

 jaw. TG, deciduous grinding tooth of lower jaw. TK, permanent grinding tooth of 

 lower jaw. TM. tooth papilla. TW, tongue. TT, enamel organ. ZO, zygoma. V, 

 mandibular branch of trigeminal nerve. 



blood being returned by veins in connection with the iris. This 

 vascular investment to the lens is merely a provisional structure, 



