20 



THE ANATOMY OF VERTEBEATED ANIMALS. 



mucous membrane acquires a larger surface, are the tur- 

 hinals. 



Riblike cartilaginous rods appear in the first, second, 

 and, more or fewer, of the succeeding, visceral arches in all 

 but the lowest Vertebrata. The upper ends of the first and 

 second of these become connected with the auditory capsule, 

 which lies immediately above them. 



The first visceral arch bounds the cavity of the mouth 

 behind, and marks the position of the mandible or lower jaw. 

 The cartilage which it contains is termed Meckel's cartilage. 



The cartilaginous rod contained in the second visceral 

 arch of each side is the rudiment of the hyoidean apparatus. 



Fig. 8. 



Fig. 8. — Under-view of the head of a Fowl at the seventh day of in- 

 cubation. — la, the cerebral hemispheres causing the integument to 

 bulge ; a, the eyes ; <?, the olfactory sacs ; k, the fronto-nasal process ; 

 /, the maxillary process ; 1, 2, the first and second visceral arches ; 

 X, the remains of the first visceral cleft. 



Like the preceding, it unites with its fellow in the ventral 

 median line, where the so-called "body "of thehyoid arises. 

 A ridge, continued forward from the first visceral arch 

 to the olfactory sac (Fig. 4, F ; Fig. 8, 1), bounds the mouth 

 on each side, and is called the maxillary pi-ocess. A carti- 

 laginous palato-pterygoid rod, developed in this process, 



