468 SPECIAL HISTOLOGY. 



as may be very distinctly perceived in small animals. All the 

 subsequent branches, both of the anterior and posterior main 

 divisions, as well as their further continuations, are consequently 

 of a mixed nature, formed of portions derived from both roots ; 

 a condition which they retain up to their ultimate distribution. 

 Here, however, an alteration takes place, the motor fibres going 

 off in by far the larger proportion into the muscular branches, 

 and the sensitive chiefly to the cutaneous. TYTiere the ganglion- 

 fibres which arise in the spinal ganglia are distributed, cannot 

 be ascertained anatomically. When their physiological relations, 

 however, are considered, it would appear as by far the most 

 probable supposition, that they do not, as at first sight one 

 would be inclined to suppose, join the sympathetic in the rami 

 communicantes, but, that accompanying the spinal nerves, they 

 are continued chiefly into the vascular branches, and consequently 

 are distributed in the integuments, muscles, bones, joints, ten- 

 dons, and membranes {periosteum, pia mater, &c), but also, 

 perhaps, to the glands and involuntary muscles of the skin. 

 The nerve-fibres in the main trunks of the spinal nerves present 

 the same diameter as in the roots, that is to say, there are finer 

 and thicker tubes, and a certain number of intermediate forms; 

 but, as they proceed, the fibres separate, the thicker going 

 more to the muscular branches, and the thinner into the 

 cutaneous nerves. According to the statements of Bidder aud 

 Volkman, the proportion of the fine to the thick fibres is, in 

 Man, as 1. 1 : 1, in the muscular nerves as 0. 1 — 0*33 : 1 ; 

 statements which I can but confirm, adding to them, that the 

 nerves of the bones contain, in the trunks, one third of thick 

 and two thirds of fine, whilst those of the articulations, 

 tendons, and membranes, exhibit a great preponderance of fine 

 fibres. In my opinion, most of the fine fibres contained in the 

 branches of the spinal nerves must be regarded as derived from 

 the spinal cord, and as being, in their function, quite of equal 

 importance with the thick fibres, and, at present, the only 

 tiling that remains unascertained, is whether they all ascend to 

 the brain, or perhaps in part arise in the spinal cord ; upon 

 which point reference may be made to § 112. 



The spinal nerves are composed in general of parallel 

 tubes, for the most part undulating, upon which circumstance 

 their transversely banded aspect depends ; they exhibit, 



