17. Hyomandibular. 18. Symplectic. 19. Quadrate. 20. Pterygoid. 21. Palatine. 22. Mesopterygoid. 23. Metapterygoid. 24. Preopercle. 25. Opercle. 26. Subopercle. 27. Interopercle. 28. Articular. 29. Angular. 30. Dentary. 31. Maxillary. 32. Premaxillary. 33. Interhyal. 34. Epihyal. 35. Ceratohyal 36. Basihyal. 37. Glossohyal. 38. Urohyal. 39. Branchiostegal. 49. Preorbital. 50. Suborbital. 51. Nasal. 52. Supratemporal. 53. Post-temporal. 54. Supraclavicle. 55. Clavicle. 56. Postclavicle. 57. Hypercoracoid. 58. Hypocoracoid. 60. Actinosts. 61. Pectoral fin. 62. Pelvic girdle. 63. Ventral fin.] The upper jaw of the shark is formed from the anterior portion of the palatine bones, which are not separate from the quadrate, the whole forming the palato-quadrate apparatus. In the himæra and the dipnoans this apparatus is solidly united with the cranium. In these fishes the true upper jaw, formed of maxillary and premaxillary, is wanting. [Illustration: FIG. 27.--Lower jaw of _Amia calva_ (Linnæus), showing the gular plate.] _The Lower Jaw._--The lower jaw or mandible is also complex, consisting of two divisions or rami, right and left, joined in front by a suture. The anterior part of each ramus is formed by the _dentary bone_ (30), which carries the teeth. Behind this is the _articular bone_ (28), which is connected by a joint to the _quadrate bone_ (19). At the lower angle of the articular bone is the small _angular bone_ (29). In many cases another small bone, which is called _splenial_, may be found attached to the inner surface of the articular bone. This little bone has been called coronoid, but it is doubtless not homologous with the coronoid bone of reptiles. In a few fishes, _Amia_, _Elopidæ_, and certain fossil dipnoans, there is a bony gular plate, a membrane bone across the throat behind the chin on the lower jaw.