This system is not as abundantly spread out in the economy as the preceding. The whole mass which it forms, compared with the whole of the other, which is more than one third of the body, presents in this respect a very remarkable difference. Its position is also different; it is concentrated, 1st, in the thorax, where the heart and œsophagus belong to it; 2d, in the abdomen where the stomach and intestines are in part formed by it; 3d, in the pelvis where it contributes to form the bladder and even the womb, though this belongs to generation, which is a function distinct from organic life. This system then occupies the middle of the trunk, is foreign to the extremities, and is found far from the action of external bodies, whilst the other superficially situated, forming almost alone the extremities, seems, as we have said, almost as much destined in the trunk to protect the other organs, as to execute the different motions of the animal. The head contains no part of the organic muscular system; this region of the body is wholly devoted to the organs of animal life.
ARTICLE FIRST.
OF THE FORMS OF THE MUSCULAR SYSTEM OF ORGANIC LIFE.
All the muscles of the preceding system take in general a straight direction. These are all on the contrary curved upon themselves; all represent muscular cavities differently turned, sometimes cylindrical as in the intestines, sometimes conical as in the heart, sometimes rounded as in the bladder, and sometimes very irregular as in the stomach. No one is attached to the bones; all are destitute of tendinous fibres. The white fibres arising from the internal surface of the heart, and going to be attached to the valves of its ventricles, have by no means the nature of the tendons. Ebullition does not easily reduce them to gelatine; desiccation does not give them the yellowish appearance of these organs; they resist maceration longer than them.
It is in general a great character that distinguishes the muscular organic system from that of animal life, that it does not arise from, nor terminate in fibrous organs. All the fibres of this last are continuous either with tendons, or aponeuroses or fibrous membranes. Almost all those of the first go on the contrary from the cellular texture, and return to it after having run their course. I at first thought that the dense and compact texture which is between the mucous membrane and the fleshy fibres of the intestines, the bladder, the stomach, &c. was an assemblage and net-work of many small tendons corresponding to these fibres, and interwoven in the form of an aponeurosis; the density of this layer deceived me at first view. Ebullition, maceration, and desiccation have since taught me, that this layer, completely foreign to the fibrous system, should be referred, as Haller has said, to the cellular, which is only more dense and compact there than elsewhere. It is this layer, which I have designated, in the cellular system by the name of the sub-mucous texture. Many fibres of the system of which we are treating appear to form an entire curve, which is not crossed by any cellular intersection; some layers of the heart exhibit this arrangement, which is in general very rare; so that there is almost always an origin and termination of the fibres, upon an organ of a nature different from their own.
We can hardly consider in a general manner the forms of the system of which we are treating; each organ belonging to it is moulded upon the form of the viscus to the formation of which it contributes. In fact, the organic muscles do not exist in distinct fasciculi, like those of animal life; all, except the heart, form but a third, a quarter and often even less in the structure of a viscus.
The greatest number has a thin, flat and membranous form. There are layers more or less broad, and hardly ever distinct fasciculi. Placed at the side of each other, the fibres are rarely one above another; hence it happens that occupying a very great extent, these muscles form however a very small volume. The great gluteus alone would be larger than all the fibres of the stomach, the intestines and the bladder, if they were united like it into a thick and square muscle.
ARTICLE SECOND.
ORGANIZATION OF THE MUSCULAR SYSTEM OF ORGANIC LIFE.
The organization of the involuntary muscles is not as uniform as that of the preceding. In these all is exactly similar excepting the differences of the proportion of the fleshy fibres to the tendinous, of the length of the first, of the prominence of the fasciculi, of their assemblage into flat, long or short muscles; in whatever place we examine them, their varieties are in their forms and not in their texture. Here on the contrary, there is in this texture marked differences; the heart compared with the stomach, the intestines with the bladder are sufficient to convince us of this. It is by virtue of these different textures, that the contractility and sensibility vary as we shall see in each muscle, that the force of the contraction is not the same, and that life is different in each, whilst it is uniform in all those of animal life. We shall now consider in a general manner the organization of the involuntary muscles.