244 THE FIFTH DAY. [CHAP. 



MeckeUs cartilage (Fig. 79, mk.) ; it soon becomes 

 covered by investing (membrane) bones which form 

 the mandible ; and its proximal end ossifies as the 

 articulare. 



FIG. 79. 



VIEW FROM BELOW OF THE PAIRED APPENDAGES OF THE SKULL 

 OF A FOWL ON THE FlFTH DAT OF INCUBATION. (From 



Parker.) 



cv. 1. cerebral vesicles, e. eye. fn. fronto-nasal process, n. nasal 

 pit. tr. trabeculse. pts. pituitary space, mr. superior 

 maxillary process, pg. pterygoid. pa. palatine, q. quad- 

 rate, mk. Meckel's cartilage, ch. cerato-hyal. bh. basi- 

 hyal. cbr. ceratobranchial. ebr. proximal portion of the 

 cartilage in the third visceral arch. bbr. basibranchial. 

 1. first visceral cleft. 2. second visceral cleft. 3. third vis- 

 ceral arch. 



In the next arch, usually called the second visceral 

 or hyoid arch, there is a very small development of 

 cartilage. This consists of a central azygos piece, the 



