These muscular and fibrous elements of the gravid uterus are arranged in numerous thin lamellm, a good view of which may be obtained by cutting a thin slice perpendicu larly out of the walls of the uterus at term.
By gentle traction, the larnince may be drawn partly asunder. They are then seen to be most densely and closely united towards the inner and outer surfaces, but to be more easily separable in the centre or vascular layer, where the laminw are connected by a looser fibrous tissue, and are everywhere permeated by numerous large and srnall venous canals. These laminae are superimposed the one upon the other, in layers parallel with the two sur faces of the uterine walls, but neither the laminw themselves, nor the fibres composing them, can be said to take any definite course. Within the laminw the fibres are arranged in flat bundles, which cross in all directions, as in the unimpregnated organ, but can seldom be traced in the same direction for any con siderable distance. This is especially the case in the middle or vascular layer. In the superficial laminm, the tendency of the fibres is to converge towards the angles to which the appendages are attached, while internally an apparent disposition to the formation of concentric circles around the orifices of the Fallopian tubes has been sometimes observed upon inverting the organ after labour. But nothing like a continuous arrangement of muscular fibres in the form of circular or longitudinal bands surrounding or investing the organ, can anywhere be demonstrated by the aid of the microscope.
The blood-vessels of the uterus undergo a marked increase in length, and especially in breadth, during pregnancy. The arteries pur sue a remarkable spiral course whilst tra versing the uterine walls. The veins form flattened channels between the muscular la minm. The enlargement of the latter is ac companied partly by a growth of the muscular fibre cells already existing in their tunica media before pregnancy, and partly by a trans formation of their inner and outer coats. Kiilliker has observed, that in the fifth and sixth month, the fibres of the middle coat un dergo an enlargement as considerable as those of the uterine walls, so that between these two scarcely any difference can be discerned. But besides these, both the inner coat, from the epithelium outwards, and the outer coat, acquire muscular fibres, which, except that they take a long,itudinal direction, do not otherwise differ from those of the middle coat. This structure is found in the trunks of the uterine veins within the broad ligament, in the internal spermatics, and in all the veins of the uterine substances, which exceed 2"' in diameter. In the smaller veins the muscu
lar layer becomes less developed. Still, in those of I"' in diameter, a longitudinal layer of muscular fibre next the epithelium may be found. The only exceptions consist of those veins which, in the placental region, penetrate the inner layers of the uterus, to become con tinuous with the maternal veins of the pla centa. These, notw ithstanding their great width, instead of containing three, possess only one layer of muscular fibre, which, toge ther with the epithelium, composes the entire coat of the vein.* Do the nerves of the uterus enlarge or mul tiply during pregnancy?—This question, which once excited much controversy, has lost its chief physiological interest, since it lias been determined that if any enlargement of the uterine nerves take place during pregnancy, this is nearly or entirely confined to the neuriletnma, or fibrous nerve sheaths. Upon this point all observers are nearly or entirely agreed. Dr. Robert Lee states*, that vihilst engaged in making dissections of the gravid uterus, he " discovered that the neurilernma was the constituent tissue of the ganglia and nerves which chiefly enlarged during preg nancy." Dr. Hirschfeld remarks, " this in crease of volume does not occur in the nervous tubules but in the neurilemma." Jobert de Lamballe having traced the nerves of the uterus in man and animals, both in the unimpregnated and gravid state, says, that he " never observed any modification of their physical condition. They appeared more voluminous in conseguence of an in filtration of the cellular tissue which sur rounds them, but they had not undergone any actual enlargement." Dr. Snow Beck removed the neurilemma, leaving only the bundles of nerve fibres or nerve tubules. On comparing the nerves of the gravid uterus with those of the unimpregnated organ, both dissections having been simi larly conducted, he found that " the size of the nerves in both dissections is essentially the same ; and when the nerves are carefully compared, no doubt is left that the nerves of the gravid uterus have undergone no change in size, nor any change in position, except that consequent upon the development of the organ." But the neurilemrna consists entirely of fibrous tissue, such as is common to most other parts of the body. It exhibits no struc tures specially nervous. Its offices, in rela tion to nerves and ganglia, are to support, protect, and bind together the nerve tubules and ganglionic nerve corpuscles.