244 THE FIFTH DAT. [CHAP. 



Meckel's cartilage (Fig. 79, mk); it soon becomes 

 covered by investing (membrane) bones which form 

 the mandible; and its proximal end ossifies as the 

 aHiculare. 



Fio. 79. 



View from below of the Paired Appendages of the Skull 

 OF A Fowl on the Fifth Day of Incubation. (From 

 Parker.) 



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

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

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

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

 hyal. dir. ceratobranchial. ehr. proximal portion of the 

 cartilage in the third visceral arch. bhr. 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 



