OF THE MEDULLARY TISSUE OF THE BONES. 143 



membrane. The pores of the compact substance appear to 

 contain them also. 



175. The fat of the bones is called marrow, in the medul- 

 lary canal, medullary fluid, in the spongy substance, and oily 

 juice in the compact substance. This fat is formed of the same 

 elements as all other fat, varying, however, in the propor- 

 tions, being more fluid ; it is also more highly coloured and 

 yellower. 



176 The medullary membrane is sensible. Duverney has 

 well pointed out the experiment, which proves this property, 

 that Bichat has, perhaps, exaggerated a little, but which it is 

 wrong to question. If, in fact, in the generality of the amputa- 

 tions performed upon man, the impression caused by dividing 

 the bone is hardly felt, it is owing solely to the more violent 

 pain, resulting from the section of the skin which has preceded 

 it. But if in a living animal, we allow a sufficient interval to 

 elapse between the section of the teguments, and the lesion of 

 the marrow, so that the impression produced by the first, may 

 have time to be dissipated, a stylet introduced into the medul- 

 lary canal, produces a pain on the instant, which is testified by 

 the animal in various ways; it will easily be supposed, that 

 this sensibility resides in the membrane, and is foreign to the 

 marrow itself. The nerves in the bone accompanying the prin- 

 cipal medullary artery, if the bone is amputated above the en- 

 trance of this vessel, the remaining marrow no longer has any 

 communication with the nervous centre; it is to this disposi- 

 tion that is attributable, the difference of sensibility observed 

 by Bichat, between the centre, and the extremities of the me- 

 dullary cavity, and also to the fact, that the nervous threads 

 proceed in dividing themselves towards the two ends of this 

 cavity. The medullary tissue is gifted with an obscure con- 

 tractility, similar to that of the cellular tissue. The arteries, 

 which ramify in this membrane, secrete and deposite the fat. 



177. The medullary membrane, according to Bichat, has 

 an early origin, pre-existent to the canal, it is filled with a car- 

 tilaginous substance, which afterwards gives place to the mar- 

 row, as fast as ossification advances. The most attentive ob- 

 servation has discovered no arteries, veins, nor medullary 

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