SPINES. 



621 



filaments confluent with a common central pith. In the Peccari 

 the pith of the coarse body-hair is crossed by condensed cells like 

 beams strengthening the cortex. The colour of the hair is lost 

 by age in Man, and during the winter season in the annually 

 renewed covering of many arctic Mammals : the endosmotic 

 transfer of their contents from cell to cell of the pith effects this 

 change. The hairs of the Cape-Mole are peculiar for the 

 iridescent tints they reflect, whence its generic name, Chryso- 

 chloris. 



The stiffer, thicker kinds of ( hair ' are called ' bristles : ' when 

 these attain unusual length, grow from the lips, cheeks, and other 

 parts of the head, and have the matrix supplied by unusually 

 large nerves, endowing them with tactile or exploratory faculties, 

 they are termed ' whiskers ' or ( vibrissae M : those which beset the 

 muzzle of the Walrus attain the thickness and stiffness of spines, 

 and serve, also, mechanical uses. 2 

 The muscles moving; vibrissae 

 have the striped fibre. 



§ 361. Spines. — Over the major 

 part, including the more exposed 

 surfaces, of the skin of the Hedge- 

 hogs (Erinaceus, Centetes) spines 

 are developed in such numbers and 

 of such length as to conceal the 

 hairs ; they are nearly straight, 

 terminate in a point, and, when 

 fully formed, are smaller at the 

 root than in the shaft. They 

 have a thick, stiff, horny cortex, 

 including a pith of cells ar- 

 ranged in transverse groups, fig. 

 488, a. The matrix is originally 

 situated beneath the derm, in con- 

 tact with the strong 'panniculus 

 carnosus;' but section of the skin 

 shows the roots and sheaths of the quills, extending to different 

 depths according to the period of their growth: the newly 

 formed ones are lodged deep, and terminate without contracting, 

 the pulp being large and active, and the cavity containing it of corre- 

 sponding size; but as the growth of the quill proceeds, the reflected 

 integument forming the sheath gradually shortens and draws the 

 quill nearer the surface ; the pulp is at the same time progres- 



1 xx. vol. iii. p. 245. 2 lb. p. 246. 



Section of skin, with spines, of Hedgehog : 

 a, section of spine magn. 



