FOSSIL REPTILES. 219 



and fills the cavity of the old one, compresses its substances 

 against the sides of the alveolus, destroys its consistence, splits 

 it and disposes it to detach itself to the level of the guna at the 

 slightest shock. The fragments which remain in the alveolus 

 are afterwards easily expelled by the forces of living nature. In 

 the crocodiles that change their teeth rings are often found thus 

 formed in the alveolus by the remains of the old and broken 

 teeth, and through which the new ones begin to shoot ; and the 

 same is observed, as we shall see presently, in the fossil jaws of 

 true crocodiles. 



Very frequently, the basis of the cone of the tooth is not 

 entire, and a notch is observable in it on the side next the inside 

 of the jaw. This proceeds from the germ having been formed a 

 little on the inside of the alveolus, and commencing from this 

 side to hinder the continuance of the old tooth. Sometimes 

 tliere are two of these, for a second germ will sometimes be 

 found before the fall of the tooth which is in place. 



The hyoi'd bone in crocodiles is very simple. Its body 

 consists of a large and cartilaginous plate, convex below and 

 concave above. The contour of its anterior part is semicircu- 

 lar, and the posterior part, more narrow, is terminated behind 

 by a concave edge. The lateral angles of this edge ossify by 

 small degrees, but always continue embodied with the rest of 

 the cartilage, so that they cannot even be considered as ves- 

 tiges of posterior cornets. The anterior semicircular part 

 has two small notches, filled by a membrane. Behind this 

 semicircle, where contraction begins, the anterior horn is arti- 

 culated on each side. This is osseous, a little square, and 

 goes off obliquely behind and towards the top. There it is 

 terminated by a small cartilaginous appendage, which is neither 

 articulated, nor suspended to the cranium by a ligament, but 

 only by certain muscles which have some analogy with those 

 of birds. The anterior edge of the plate is raised a little at the 

 base, and forms a slight representation of an epiglottis, which 

 would be very broad and very low. On this cartilaginous plate 



