262 DENNIS, ON FOSSIL LIAS. 



mals that have the power of springing, a preponderance of 

 pointed, oval lacunae, and. it is curious in this respect, to com- 

 pare the microscopic structure of the tiger's femur with that 

 of the kangaroo, or the frog's tibia with that of the newt. 

 The toad agrees very nearly with the frog, only the lacunae 

 are longer, a character I have observed in animals that 

 climb. Those of the newt are quite dissimilar, and the struc- 

 ture of the tiger and the kangaroo is so very similar that it is 

 difficult at first to discriminate between them. The same 

 oval lacunae are present in birds, and I cannot but think they 

 indicate a power possessed by the animal, of springing. The 

 ulna of the lesser flying opossum is a very beautiful illustra- 

 tion, the bone, in the shape of its lacunae, most resembling 

 that of birds, though still retaining sufficient evidence of the 

 mammal in its character. Tlie pterodactyle, that singular 

 flying lizard, has the same pointed, oval lacunae. The bat, 

 also a flying quadruped, has the sairie ; and it is curious to 

 observe in Mr. Quekett's book that the only bird that has not 

 similar lacunae is the parrot, a bird that never springs from its 

 perch, but climbs by its bill and claws. The force and 

 rapidity with which some birds rise from the ground, as the 

 partridge does, is perfectly surprising, and is quite as won- 

 derful as the spring of the tiger, the bound of the gazelle, or 

 the flight of the opossum : but the strain upon the bones of 

 these animals must be very great, and may well account for a 

 particular and suitable structure. 



In the tarsus of a small Australian parrot, I find very few 

 of the pointed lacunae, but numerous long ones ; and in the 

 ulna of the same bird, the pointed ovals are much more nu- 

 merous. The Arctic fox, in its leg-bone, beautifully exliibits 

 the pointed oval lacunae ; so does the red Indian squirrel. 

 The same may be seen in the dog, cat, common fox, mouse, 

 &c. ; and it would appear that they are present in all bones 

 that are subject to great or violent muscular action, as a 

 bird in its flight, or a mammal and a reptile in its bound. It 

 is curious also to compare the leg-bone of the ornithorynchus 

 with that of the turtle ; for there is a very great similarity 

 between them, both in the haversian canals and the shape of 

 the lacunae ; and certainly that strange mammal does approach 

 in its habits the chelonian. 



If a very thin vertical section is taken from the same part of 

 the humerus of a kangaroo and an otter, you will observe in 

 the former numerous narrow-pointed lacunae, similar to those 

 in the tibia of the frog or in the bones of birds ; in the latter 

 you will not see one, the ovals seeming almost round. Com- 

 pare the otter with the beaver, another aquatic animal, and 



