TEGUMENT ARY ORGANS. 



505 



appears to me to be clear ; for the knob which 

 projects into the cavity of the mucous canal 

 is homologous with the central " nucleus " of 

 the Savian body, and this with the solid axis 

 of the Pacinian body,and with the corpusculum 

 tactus, so that the " tactile " sac of the Chi- 

 maera, e. g., may be said to be a tactile cor- 

 puscle which is connected with the surface of 

 the integument. 



No organ at all resembling these has cer- 

 tainly been met with, above the class of Fishes, 

 in either Reptilia or Birds, but in Mamma- 

 lia there are structures which must, I think, 

 be placed in the same category. About the 

 lips and nose of almost all mammals in fact, 

 there are certain long, strong hairs, the vi- 

 brissae or "whiskers" (fig. 321.). These in 

 their general structure resemble ordinary hairs, 

 but the sac of each, instead of lying free in 

 the enderon, is enclosed in a second thick sac, 

 composed of firm, dense, connective tissue, 

 which attains at times an almost cartilaginous 

 hardness. A looser areolated tissue connects 

 this with the outer surface of the proper hair 

 sac, and supports an abundant .vascular net- 

 work proceeding from vessels which enter at 

 the deep end of the sac. Furthermore, a very 

 considerable nerve pierces one side of the 

 " sclerotic " coat near this end, and passes to 

 the surface of the proper hair sac, upon which 

 it spreads out and forms a nervous expansion, 

 its fibrils dividing and subdividing, and so 

 terminating. 



Fig. 321. 



mammal and the fish, I think one cannot but 

 be struck with the similarity of plan between 

 their vibriss3 and the " tactile " canals. The 

 sensory impression is conveyed to the gelati- 

 nous contents of the canals in the fish by the 

 vibration of the dense medium in which it 

 lives; while in the mammal the impulse is 

 communicated by the contact of some external 

 object with a long elastic hair lever; but the 

 final arrangement for the receipt and appre- 

 ciation of the impressions is essentially the 

 same in each case, nor indeed does it differ 

 from that which is met with in the highest 

 organs of sense. 



Muscles of the enderon. In the Invertebrata 

 the great majority of the muscles are, as is 

 well known, inserted into the integument, but 

 those which are attached to the chromato- 

 phora of mollusks and to the spines of an- 

 nelids and other worms, might be regarded 

 as belonging more especially to the integu- 

 mentary system. 



In Fishes and Reptiles the superficial layer 

 of striped muscles of the body is always more 

 or less connected with the integument ; but 

 hitherto no unstriped fibres appear to have 

 been detected in it. In Birds, however, the 

 unstriped muscles attain a very great develop- 

 ment, forming a thick layer whose bundles (c) 

 run between and are attached to the sacs of 

 the feathers (Jig. 322.). 



Fig. 322. 



Vibrissa from the snout of the Mouse, 

 a, " sclerotic " sac ; 6, hair-sac ; c, nerve-trunk ; d, 

 muscular fibres. 



Considering the different habits of life of the 



Pacinian body (6) and feather-sac (a) from the 

 base of the mandible of a pigeon, c, muscles of 

 the feather sacs. 



In the majority of Mammals there is a 

 special teguraentary striped muscle, which 

 attains an enormous development in the 

 hedgehog, while a mere rudiment of it remains 

 in man, as the platysma myoides. Here, 

 however, the striped "peaucier" muscle is 

 replaced by the unstriped bundles which, as 

 Kolliker has shown, run from the upper layer 

 of the enderon to the bases of the hair sacs, 

 and effect the various movements of which 

 the hairs are capable. 



