Now the real point of interest to be de termined is, whether during pregnancy the innervation of the uterus is increased in any degree proportionate to the augmented supply of blood to the organ. But the neurilemma has never been regarded as either a generator or conductor of nerve force, the former pro perty belonging exclusively to the nerve centres, and the latter to the nerve tubes or nerve fibres. It is therefore necessary to as certain if either nerve centres or nerve fibres become in any way multiplied or enlarged during the process of utero-gestation.
Regarding a new formation of nerve centres, there is at present no anatomical proof that any fresh ganglionic corpuscles are formed during pregnancy within the ganglia or plexuses from which nerves proceed to the uterine tissues.
Regarding the changes which take place in the nerve tubes or fibres during gestation, much interesting information is obtained from the researches of the late Dr. Franz M. Kilian, who devoted a considerable time to the in vestigation of this point. Dr. Kilian dis covered, that in the unimpregnated uterus a successive diminution of the nerve fibre, whether in bundles or isolated, takes place as it approaches the point of distribution. If broad, the fibre, after a certain portion of its course, begins to lose its greater breadth, dis tinct double contour, and strongly marked granular contents, and then continuing as a pale fibre of intermediate size until it ap proaches nearer to the uterus, it ultimately assumes an embryonic character ; that is, the extremely attenuated pale-margined fibre which traverses the tissues as a slender trans parent band, has ceased to form a cylinder filled with nerve granules, and constitutes now only a pale slender stripe, or empty non• medullated sheath. 'Within this empty sheath there still occur, at distant intervals, little collections of granular fatty contents.
Now, in the early periods of pregnancy these embryonal forms are observed to be come gradually more distinct between the muscular fibres, and at a later period many of the fine tubes become filled with medulla, which was wanting in the unimpregnated con dition ; the little collections of granular fatty contents just mentioned constituting the commencement of the nerve cylinders. For it is by the confluence of these isolated drops within the sheath that the medullated cylinder is formed, so that medullated fibres not only proceed as far as the uterus, but also become developed with continually increasing dis tinctness during pregnancy between the mus cular fibres.
These observations correspond exactly with changes which Kilian observed to take place also in young animals, when the nerve fibres in the neighbourhood of the uterus are all in the embryonic condition, but become gradually medullated up to a certain point, in propor tion as the development of the animal pro ceeds, so that the nerves may be said to grow forward in the direction of the uterus.
It should be understood, however, that in all these cases, the dimension of the nerve fibre never exceeds that of the branch whence it is derived, but that, on the contrary, a law of gradual diminution of the nerve is found to obtain in all cases, although the changes now described cause the rate of this to be different in the unimpregnated and gravid uterus respectively.
Kilian had no opportunity of examining the condition of the nerves in the human uterus at different periods of pregnancy, but he doubts not that the alterations are analogous to those which he found in animals.
7'he lining 2nembrane of the uterus. _Develop ment of the deeidua.— The last, and at the same time the most interesting, transforma tion of the uterine tissues remains to be de scribed. It is that which takes place in the lining membrane, and which has for its object the formation of an immediate covering and protection to the ovutn. By the aid of this membrane, the fertilised ovum, on arriving loose in the uterine cavity, is re-attached to the parent body, and is enabled to receive from it the supplies necessary for nutrition and growth.
But before the ovum enters the cavity of the uterus, the lining membrane of the latter swells and becomes softer and at the same time more vascular.* This augmentation in bulk of the uterine inner coat takes place in almost all cases when an ovum has been fer tilised. That it does not depend upon the presence of the ovum in the uterus, is proved by the fact, that in cases of extra-uterine ges tation, with rare exceptions, a developntent of decidua occurs within the uterus, forming there,'in some cases, a more profuse growth even, relatively' to the size of the uterus, than takes place in ordinary gestation.