| OCR Text |
Show I~· 57 - 1 rnt of the head ot a c Ili.C 1'•· - r' rr, rrpr , , tg. . . , ' tlrce siv , stap;t>s nf 1t heI t1 ·.~ ccl o•sp. mr• t ' '<'-.'tc le of tlt cel'ehral hemi sphel' s ; ' fill.S t , ""'' econd ' and tltinl eel'e Ira ve:st THE DT~VELOPMENT OF TilE FOWL' SKULh 139 ventricle tho rudimentary pineal gland (e) makes it.s appearance in the middle line. From the middle of the lower wall grows out a process, tho infundibulum, terminating in a glandular appendage, the pituitary body, which last is lodged in the deep fossa situated in the floor of tho anterior division of the skull, i1nmediately in front of, and beneath, the termination of the notochord (Fig. 57, B, D, d). The three pairs of sensory organs appertaining to the highe1· senses,-tbe nasal sacs, the eyes, and the ears,-arise as simple cmcal iuvolutions of the external integument of the head of the embryo. That such is the case, so far as the olfactory sacs are concerned, is obvious; and it is not difficult to observe that the lens and the anterior chamber of the eye are produced in a perfectly s.lmilar manner. It is not so easy to see that tho labyrinth of the ear arises in this way, as the sac resulting from tho involution of the integument is small, and remains open but a very short time (Fig. 57, 0, b). But I have so frequently verified Huschke's and Remak's statement that it does so arise, that I entertain no doubt whatever of the fact.* The outer ends of the olfactory sacs rmnain open, but those of the ocular and auditory sacs rapidly close ·up, and shut off their contents fi-om all direct communication with the exterior. The olfactory nerve is developed from the anterior division of the anterior cerebral vesicle. The optic nerve is primarily developed from the posterior division of that vesicle, its connection with the middle vesicle (which ev ntually gives ri e to thE> c01-pora quadrigemina) vesicle of the third ventricle; a, rudiments of the eyes and optic nerves ; b, of the ears; g, of the olfactot y organs ; d, the infundibulum; e, the pineal gland; c, protovertebrro; lt, notochord; 1, 2, 3, 4, 5, visceral arches; V, VII, VII!, the trigeminal, portio dnra, and eighth pair of cranial nerves; ll, the fi·onto-nasal procc:,s; l, the maxillary process ; :r, the f-Irst visreral cleft. · CA,, sBid,e u\'pipewer aatn dtl tue ntdheirrd v ideawy.s of the head of a chick at the end of the second day. D, side view at seventy-five houl's. E,.s sliidgeh tv ipelw'es osufr eth. e head of a chick at the firth day, which has been subjected to F, head of a chic)~ at the sixth day, viewed from below. l<I, tlte ~rtilaginous crauium of the same. P, Gpoi,t uciotach•·lyea s. pace; tr, trabeculw; Qu, quad>-.te cartilage; Be, seuticirculm· cnnn!.<; G, head of a chick at the seventh day, from below. * Soc al. o Kollikor's "Entwjrkolnngs Gcschiolttf'," p. 300, et seq. |
