20 THE DERMOSKELETOX. 



by a casque of the same ; and the tail is encased in a sheath 

 of similar interlocked ossicles. To allow of the requisite 

 movements of the trunk in the small existing armadillos, 

 which, when attacked, roll themselves into a ball, from 

 three to nine transverse rows of the dermal bones, h h, 

 are interposed, having a yielding elastic junction with 

 each other, and with the anterior, o o, and posterior fixed, 

 and larger, parts of the trunk-armor ; and by this modifi- 

 cation the head and limbs can be withdrawn beneath the 

 armor, when its parts are pulled together by the strong 

 cutaneous muscles into a hemispheric form. In South 

 America, to which continent the armadillos are peculiar, 

 remains of gigantic quadrupeds, similarly defended, have 

 been discovered in the more recent tertiary deposits ; but 

 in these colossal armadillos (Glyj^todon) the trunk-armor 

 was in one immovable piece, covering the back and sides, 

 and was not divided by bands. Besides the defence which 

 such a modification of the integuments would afford 

 against the attacks of predatory animals, the armadillos 

 and glyptodens habitually frequenting the great forests 

 of South America may have been protected by the same 

 hard, arched covering from falling timber. 



Such are some of the instances of the structure and 

 uses of the dermoskeleton in the vertebrate province. 

 The development of this system of the skeleton is not 

 dependent on the grade of organization, for we find it in 

 the highest and in the lowest classes ; nor does a great 

 amount of osseous matter in the skin necessarily involve 

 a small amount or absence of the same matter in the 

 deeper-seated skeleton ; for all the parts of this system of 

 bones, a, c, d, m, 7is, are as well developed and as well 

 ossified in the armadillos as in the quadrupeds which are 

 covered by hair. The different states of the neuroskele- 



