AMPHIBIA. 183 



which touches the external end of the palatine in front. The 

 other two rays are shorter. One of them runs inwards, the other 

 along the under side of the quadrate cartilage. A T-shaped bone, 

 the squamosal, the stem of which covers the quadrate cartilage, 

 partly covers the auditory region. This bone supports the annular 

 tympanic cartilage, over which the tympanic membrane is stretched. 



(/5) The lower jaw (mandible) consists of two strongly-curved 

 halves, each of which is traversed by an axial cartilage, Meckel's 

 cartilage, ossified in front into a small mento-meckelian bone, uniting 

 with its fellow in a median symphysis. Behind it presents an 

 oval projection, the condylc, which articulates with the quadrate 

 cartilage. Meckel's cartilage is strengthened below and on its 

 inner side by a long angulo-splenial bone, from the posterior part 

 of which a small elevation, the coronoid process, projects upwards. 



Each half of the mandible possesses a membrane-bone, the 

 dentary, which is a thin splint covering the outside of Meckel's 

 cartilage for rather more than its anterior third. 



A series of structures forming the hyoid apparatus are con- 

 nected with the skull, and usually described with it. They are 

 partly related to the auditory apparatus, and partly to the floor 

 of the mouth. The columella is a small rod, bony in the centre, 

 which is fixed into the fenestra ovalis by one end, while the 

 other is attached to the inside of the tympanic membrane. The 

 remainder of the hyoid consists of a quadrangular plate of cartilage, 

 the body of the hyoid, supporting the floor of the mouth. Its angles 

 are produced into anterior and posterior processes. In front of 

 the former two slender, curved rods of cartilage, the anterior cornua, 

 arise, each of which runs backwards round the angle of the mouth 

 to be attached to the auditory capsule just beneath the fenestra 

 ovalis. From the posterior end of the hyoid body two short bony 

 posterior cornua or thyrohyals run back, which diverge and enclose 

 between them the laryngo-tracheal chamber. 



(7>) The vertebral column is a hollow rod running back from 

 the skull along the dorsal side of the body. The spinal cord lies 

 in its cavity. The anterior part of the column is segmented, 

 being made up of nine rings, the vertebrce, while the posterior 

 part, termed the urostyle, is unsegmented. All are cartilage 

 bones. 



The vertebra are very similar, except the first and last. Each 

 is a ring, the thickened ventral part of which is the body or centrum, 



