SKELETON OF THE CROCODILE. 113 



purposely subdivided element have received definite 

 names. That numbered 29, which offers the articular 

 concavity to the convex condyle of the tympanic, 28, is 

 called the "articular" piece; that beneath it, 30, which 

 develops the angle of the jaw, when this projects, is the 

 "angular" piece ; the piece above, 29', is the " surangular ;" 

 the thin, broad, flat piece, 31, applied, like a splint, to the 

 inner side of the other parts of the mandible, is the 

 "splenial;" the small accessory ossicle, 31', is the "coro- 

 noid," because it develops the process, so called, in lizards; 

 the anterior piece, 32, which supports the teeth, is called 

 the " dentary." This latter is the homotype of the pre- 

 maxillary, or it represents that bone in the mandibular 

 arch, of which it may be regarded as the haemal spine ; 

 the other pieces are subdivisions of the hasmapophysial 

 element. The purport of this subdivision of the lower 

 jaw-bone has been well explained by Conybeare^ and 

 Buckland,^ by the analogy of its structure to that adopted 

 in binding together several parallel plates of elastic wood 

 or steel to make a crossbow, and also in setting together 

 thin plates of steel in the springs of carriages. Dr. Buck- 

 land adds: "Those who have witnessed the shock given 

 to the head of a crocodile by the act of snapping together 

 its thin long jaws, must have seen how liable to fracture 

 the lower jaw would be, were it composed of one bone only 

 on each side." The same reasoning applies to the com- 

 posite structure of the long tympanic pedicle in fishes. 

 In each case the splicing and bracing together of thin flat 

 bones of unequal length and of varying thickness, affords 

 compensation for the weakness and risk of fracture that 



1 "Geol. Trans.," 1821, p. 565. 



2 "Bridgewater Treatise," 18B6, voL i. p. 170, 



10^ 



