DEVELOPMENT OF THE NOSE. 



243 



This pair of nasal grooves, as well as the single mouth 

 groove (Fig. 235, m), is lined by the horn-plate. The 



Fig. 232. 



Fig. 233. 



Z. 



Fig. 235. 



Fig. 236. 



Figs. 232, 233.— Head of an embryonic Chick, on the third day of 

 incubation : 232, from the front ; 233, from the right side, n, Nose-rudi- 

 ment (olfactory grooves) ; Z, eye-rudiment (sight-grooves) ; g, ear-rudiment 

 (auditory grooves); v, fore-brain ; gl, eye-slits; o, upper jaw process; u, 

 lower jaw process of the first gill arch. 



Fig. 234. — Head of an embryonic Chick, on the fourth day of incubation, 

 from below : n, nose-groove ; o, upper jaw process of the first gill arch ; 

 u, lower jaw process of the same ; k", second gill-arch ; sp, choroidal fissure 

 of the eye ; s, throat (pharynx). 



Figs. 235, 236.— Two heads of embryonic Chicks : 235, at the end of the 

 fourth day; 236, at the end of the fifth day of incubation. The letters as in 

 Fig. 234. Additional letters are in, inner, and an, outer nasal process; nf, 

 nasal furrow ; st, frontal process ; m, mouth-cavity. (After Koelliker.) 



All these figures are proportionately enlarged. 



