ELASTICITY 



the genera Dnsypus and Tututia, comprcheixt- 

 ni'j tin' Armadillos, and in Chlaniy/i/iorus, ex- 

 Inliits various modificalions of a very extraordi- 

 nary nature. The body of the Manit is co- 

 vered with large imbricated scales, of a more 

 or less rhornboidal form, of a horny consistence, 

 and a reddish brown colour. The true struc- 

 ture of these scales is undoubtedly a congeries 

 of hairs, as is evinced in the longitudinal 

 lines with which they are all marked. Theyform 

 a very firm and complete protection to the 

 animal when rolled up in a ball, which is its 

 ordinary means of escaping from danger. The 

 scales cover the whole surface, excepting the 

 inferior part of the head and tail, the axillae, 

 the middle of the belly, the inner surface of the 

 thighs, and the soles of the feet, all of which 

 parts, excepting the latter, are furnished with a 

 few scattered hairs. In the Armadillos an 

 ossemis crust or shell envelopes the whole of 

 the upper part of the head and the body, the 

 outer part of the limbs, and the whole of the 

 tail. The inferior parts of the body are not 

 thus protected, but scantly covered with hair, 

 intermixed with a kind of hard warts or scales. 

 Their armour is composed of a helmet covering 

 the upper part of the head, of a buckler over 

 the shoulders, a similar one over the crupper, 

 and the back has numerous imbricated bands, 

 which move upon each otlirr, varying in num- 

 ber in the different species; the tail is covered 

 by rings, also allowing of motion. It is clear 

 that this hard bony armour is capable of afford- 

 ing these animals the most complete protection 

 when coiled up, which is the position usually 

 assumed by them when in danger, or during 

 repose. Although there is mutual motion only 

 at the margins of the different pieces and at the 

 commissures of the bands, there is considerable 

 yielding at every portion of this coat of mail. 

 Each of the larger pieces is composed of nume- 

 rous adherent smaller ones, hexagonal, and per- 

 fectly tessellated ; those of the shoulders are 

 arranged in segments of concentric circles, the 

 concavity being in front, so that the anterior 

 series, which is the shortest, embraces the neck 

 of the animal. The covering of the posterior 

 part has a similar arrangement, but reversed, 

 so that the short concave margin meets the 

 origin of the tail. The cuirass of the Cliluini/- 

 phiiriin triiin-iitiix ditlcrs in many respects from 

 that of the Armadillos, and is thus described 

 by Dr. Ilarlam in the only account which we 

 have of the details of this singular animal, with 

 the exception of the very interesting descrip- 

 tion of its osteology by Mr.Yarrell, in the third 

 volume of the Zoological Journal. 



" The shell which covers the body is of a 

 consistence somewhat more dense and inflexi- 

 ble than sole leather of equal thickness. It is 

 composed of a series of plates of a square, 

 rhomhoidal, or cubical form ; each row sepa- 

 rated by an epidermal or membranous produc- 

 tion, which is reflected above and beneath, over 

 the plaies ; tire rows include from fifteen to 

 twenty-two plates; the shell being broadest at 

 its posterior half, extending about one-half 

 round the body; this covering is loose through- 



out, excepting along the spine of the back and 

 top of the head ; being attached to the back 

 immediately above the spine, by a loose arti- 

 cular production, and by two remarkable bony 

 processes; on the top of the os frontis, by 

 means of two large plates, which are nearly in- 

 corporated with the bone beneath ; but for this 

 attachment, and the tail being firmly curved 

 beneath the belly, the covering would be very 

 easily detached. The number of rows of plates 

 on the back, counting from the vertex, (where 

 they commence,) is twenty-four; at the twenty- 

 fourth the shell curves suddenly downwards, 

 so as to form a right angle with the body ; this 

 truncated surface is composed of plates nearly 

 similar to those of the back ; they are disposed 

 in semicircular rows, five in number ; the lower 

 margin somewhat elliptical, presents a notch in 

 its centre, in which is attached the free portion 

 of tail, which makes an abrupt curvature, and 

 runs beneath the belly parallel to the axis of 

 the body ; the free portion of the tail consists 

 of fourteen caudal vertebra, surrounded by as 

 many plates, similar to those of the body ; the 

 extremity of the tail being depressed so as to 

 form a paddle ; the rest of the tail compressed. 

 The caudal vertebra extend up to the top of 

 the back, beneath the truncated surface, where 

 the sacrum is bent to meet the tail. The supe- 

 rior semicircular margin of the truncated sur- 

 face, together with the lateral margins of the 

 shell, are beautifully fringed with silky hair.'' 



It is much to be regretted that but little is 

 known of the generation of these animals. The 

 dissections which have hitherto been made of 

 the more interesting forms have been imper- 

 fectly performed, or the subjects themselves 

 have been in such a condition as to allow of 

 but very incomplete observations. 



For BIBLIOGRAPHY, sec that of MAMMALIA. 



(T. Bell.) 



ELASTICITY (Germ. Springkraft, Fe- 

 derkrafl) is that property of natural bodies in 

 virtue of which they admit of change either of 

 siie or form from the application of external 

 force, resuming, upon the suspension of that 

 force, their proper shape or volume. 



Though elasticity is a purely physical pro- 

 perty, its investigation is scarcely less interest- 

 ing in physiological than in mechanical science. 

 The most cursory examination of a living body 

 is sufficient to convince us, that nature, in 

 regulating its varied functions, has availed 

 herself no less of physical than of vital laws. 

 As it is the province of the physiologist to 

 explain and analyze the several actions whose 

 aggregate is life, to trace each to its proper 

 source, and to distinguish thoe which are 

 truly vital from those which are merely mecha- 

 nical, it is plain dial an acquaintance with the 

 physical properties of the material elements of 

 living bodies becomes one of the foundations 

 of his knowledge. Hence, ill a publication, 

 the design of which is to present a complete 

 view of the structure and functions of living 



