102 ; ANIMAL PHYSIOLOGY. 
bryo itself. Fig. 114 gives appearances furnished by a vertical 
transverse section. The relations of the parts of the digestive 
tract and the mode of origin of the lungs may be learned from 
Fig. 115. 
Fria. 117,Head of chick of fourth day, viewed from below as an opaque object (Foster and 
Balfour). The neck is cut across between third and fourth visceral folds. C. H, cerebral 
hemispheres ; F. B, vesicle of third ventricle : Op, eyeball ; nf’, naso-frontal seer m, 
cavity of mouth ; S.m, superior maxillary process of F.1, the first visceral fold (mandibu- 
lar arch); F. 2, F. 3, second and third visceral arches ; NV, nasal pit. 
An examination of the figures and subjoined descriptions 
must suffice to convey a general notion of the subsequent: prog- 
Fic. 118.—Embryo at end of fourth day, seen as a transparent object (Foster and Balfour). 
CH, cerebral hemisphere ; F’. B, fore-brain, or vesicle of third ventricle (thalamencepha- 
lon), with pineal gland (Pn) projecting ; M. B, mid-brain ; Cb, cerebellum ; IV. V, fourth 
ventricle ; L, lens; chs, choroid slit; Cen. V, auditory vesicle ; sm, superior maxillary 
process ; 1F, 2F, etc., first, second, etc., visceral folds ; V, fifth nerve; VI, seventh nerve; 
G. Ph, glossopharyngeal nerve ; Pg, pneumogastric. The distribution of these nerves is 
also indicated : ch, notochord ; Ht, heart ; MP, muscle-plates ; W, wing: H. L, hind-limb. 
The amnion has been removed. Al, allantois protruding from cut end of somatic stalk SS. 
