382 SPECIAL HISTOLOGY. 



function of which appears to me to consist in the regulation of 

 the conditions of the vascular system, by their conveying to the 

 central organ (spinal chord) through the sensitive fibres intelli- 

 gence of the state of the vessels, of the quantity of nutritive fluid 

 in the bone, and probably also of the modus of the molecular 

 change going on in themselves, and by means of the motor 

 elements their bringing a reflex influence from it, to the arteries 

 and veins which are manifestly furnished with contractile 

 fibres. These unconscious and involuntary alternations of 

 influence of sensible and motor filaments, are, as it appears to 

 me, the most important phenomena of the innervation in 

 bones, as well as in all other organs, the nerves of which are 

 not constantly in relation with the external world, and make it 

 intelligible, why it is, that no organ, containing nerves 

 and vessels at all, possesses nerves of only one kind. It is 

 not, however, by this, intended to imply that the nerves of 

 bones do not convey conscious perceptions ; it is possible that, 

 through them, we obtain a certain degree of knowledge of the 

 processes going on in the bones, of the degree of fulness of the 

 vascular system, the mechanical influences to which they 

 are exposed from without in the movements caused by the 

 action of the muscles, the weight of the body or of external 

 objects, in lifting weights, mastication, &c; but in any case 

 this knowledge would be very indeterminate, and the sensation 

 excited not definitely localised, being confused in the general 

 feelings of fatigue, effort, or relaxation. On the other hand it 

 is quite certain that the bones, in man, in many diseases, and 

 in consequence of mechanical injury, afford pain, which latter 

 fact has also been frequently noticed in animals, at all events, 

 upon irritation of the larger nervous trunks of the diaphyses. 

 In man the apophyses in particular, and the vertebral and 

 cranial bones, seem readily to become painful, which is 

 explained by the considerable number of nerves immediately in 

 the spongy substance. The compact substance on the other 

 hand might probably be regarded as scarcely obnoxious to 

 pain; as, for instance, in resections, but not so perhaps the 

 periosteum, which less from its own nerves than as the vehicle 

 of those of the bones before they enter their destination, must 

 naturally be affected in the same way that they are. Whether 

 the nerves of the bones through which, perhaps, the conscious 



