SKELETON OF VERTEBRATA. 361 



cylindrical bones, composing the metacarpus (m), in 

 the former, and the metatarsus (m), in the latter 

 case. In the most complete forms of developement 

 these are always five in number in each limb ; they 

 are placed generally parallel to each other, but are 

 enveloped in one common covering of integument. 

 The Phalanges, or toes, (z), are cylindrical bones, 

 continued in a line from each of the former: they 

 are generally three in number in each toe. To the 

 last joint, which is often termed the ungual bone, 

 there is usually attached either a nail, a claw, or a 

 hoof. Small detached bones are frequently found 

 at the exterior part of the angles which they form 

 by their junction, serving the purpose of giving 

 a more advantageous position to the tendons of the 

 muscles which extend those joints. The putella, or 

 knee pan (p), is the largest of these, and is pretty 

 constantly present. Smaller bones of this descrip- 

 tion are met with on the joints of the fingers, and 

 are termed sesamoid bones. 



On comparing these divisions of the limbs of 

 quadrupeds with those of insects we cannot fail to 

 perceive that there exists between them a marked 

 analogy : and that naturalists were not led away by 

 mere fancy when they applied to the latter the 

 same names as those borne by the former. This, 

 however, is not the only instance of analogy that 

 may be discovered between the structures of arti- 

 culated and of vertebrated animals, however strong 

 may be the contrast which they ofier in all the 

 essential featuresof their conformation. The rings 

 which constitute the skeleton of the insect, and 

 which enclose its principal nervous cords, have 

 been supposed to have an analogy with the circles 



