FOWL SIXTH TO Kid I ITU DAYS 





The main purl inns <!' the skeleton !)<<, m,- laid dn\\n in 

 chondral tissue and, towards tin; end of the day, in cartilage. 



Tin; In-art brains to assume its definitive external form; the 

 ventricular septum develops and the conus septum begins to do so. 

 The fourth aortic arch becomes obliterated on the left side. 



SEVENTH DAY (Figs. 243 and 244). The mushroom--!. 

 allantois is spreading actively all round beneath the serous 

 membrane. The aumion is beginning to show waves of contraction 

 passing along its wall. The brain and eyes and consequently tin- 

 head as a whole are of relatively enormous size. In sections the roof 

 of the fourth ventricle is 

 found to be developing ir- 

 regular folds in which the 

 vessels of the choroid plexus 

 will appear. All three 

 turbinal rudiments are pre- 

 sent in the nose. The crop 

 is beginning to expand. The 

 visceral clefts are all closed. 

 The glands of the stomach 

 are beginning to make their 

 appearance as rudiments. 

 The cavity of the enteron 

 disappears for some distance 

 forwards from the point of 

 origin of the allantois. The FIG 248i _ Fowl . 8 opencd dnring tlu . sewnth (1;lv . 



Mullerian ducts Uiay Show The body of the chick is seen dimly through th.- 



incipient asymmetry. The highly vascular allantois. The vessels of the 



nOtOChord is beginning tO allantois can he distinguislMMltn,,,, th,,>, of the 



it i_ vascular area by their turning back at the edge of 



DC Constricted by the Verte- the allantois while those of the vascular area pass 



brae. The first traces of onwards uninterruptedly. The highly fluid char- 



ossification are making their ^ of th ^ is shm ; u !' y ! he V ? lk 1 ; 8ac f "t 11 



. q bulging outwards over the broken shell at th.- 



appearance, especially in the po i n t marked *. 

 skeleton of the limbs. H// .,n ail toi.s. 



The septum of the conus 



arteriosus is complete and the muscular coat extends into it from 

 each side : the pocket-valves are becoming excavated. The fourth 

 aortic arch on the left side has disappeared while the portion of 

 aortic root between arches III and IV on the right side, and U-hind 

 arch III on the left side, are becoming obliterated. 



EIGHTH DAY. The movements of the amnion now reach their 

 highest degree of activity. The fronto-nasal process (Fig. 245, C) is 

 growing out to form the pointed beak while the lower jaw is taking 

 a similar pointed form, the two mandibular arches being now con- 

 tinued into one another ventrally without a break. The rudiments 

 of feathers are beginning to make themselves apparent. 



In the brain the cerebellum is becoming folded on itself so as to 

 bulge outwards. The oro-nasal grooves are covered in to form the 



all. 



