THE SKELETON OP THE VISCERAL ARCHES. 



85 



is hard to say whetlier the styloid part of the hyoid is con- 

 tinued into the incus by these ligaments or by the stapedius. 

 But, however this may be, the tiwlleus and the incus are the 

 proximal ends of the mandibular and hyoidean arches 

 respectively. 



In osseous fishes (0, Fig. 24), which have no fenestra ovalis 

 or stapes, the supra- stapedial part of the hyoid becomes a 

 large bone — the hyomandibular. On the other hand, the 

 proximal extremity of the quadi-ate cartilage atrophies, loses 



Fig. 24. 



:rc_S.S^. 



StBC 



Fig. 24.— Diagram of the skeleton of the first and second visceral 

 arches in a Lizard (A), a Mammal (B), and an Osseous Fish (C). 



The skeleton of the first visceral arch is shaded, that of the second is 

 left nearly unshaded. /. First visceral arch. Mck. Meckel's car- 

 tilage. AH. Articulare. Qu. Quadratum. 3Ipt. Metapterygoid ; 

 31. Malleus; p.g., Processus gracilis. II. Second visceral arch. 

 Hy. Hyoidean cornu. St. H. Stylohyal. S. Stapedius. Stp. Stapes. 

 S. SAp. Supra-stapedial. i/iV/. Hyomandibular. The arrow indicates 

 the first visceral cleft. Pc. The periotic capsule. P?^. The pterygoid. 



its direct connection with the periotic capsule, and becomes 

 distinctly ossified, as the metapterygoid. In the Sharks, 

 even the ascending, metapterygoid, part of the quadrate, 

 is lost. 



The quadrate and supra- stapedial portions of the first 

 and second visceral arches coalesce in the Chinuera, Dipnoi, 

 and many Amphibia, into a single cartilaginous plate. 



In the Mammalia, and to some extent in Aves, osseous 

 matter is deposited in the fibrous tissue which suiTOunds 

 the sides and base of the tympanic membrane, and gives 

 rise to a special tympanic bone. In most Mammalia, ossifi- 



