196 Vertebrate Embryology 



process. The space between the mandibu- 

 lar arch behind, and the fronto-nasal and 

 maxillary processes in front, will be the 

 mouth of the chick 



_.{-. \ !! /OK 



oc 



BR 



FIG. 64. THE HEAD OF AN EMBRYO CHICK AT THE END 

 OF THE FIFTH DAY OF INCUBATION ; SEEN FROM BELOW. 

 (After Marshall.) Compare Fig. 72, A, for a side view of 

 an embryo of about the same age. 



BR, first branchial arch. S, cerebral hemispheres. Cff, noto- 

 chord. DS, mouth. FP, fronto-nasal process. HM, hyomandibular 

 cleft. HY, hyoid arch. MN, mandibular arch. MX, maxillary 

 arch. NS, spinal cord, seen in section where the neck has been cut 

 across. OC, eye. Off, choroid fissure. OK, olfactory pit. OL, lens. 



The relation of the parts, just described, 

 to each other may, perhaps, be made more 

 clear in the following way : with the hands 

 in front of the body, and pointing down- 

 wards, bring the tips of the fingers together, 

 the fingers of each hand being slightly sepa- 



