of the execution of these volitions, have all a regularity, a symmetry which are never found wanting.
Such, in fact, is the truth of this character, that the muscles and nerves cease to become regular, when they no longer belong to animal life. The heart, the muscular fibres of the intestines, &c. are a proof of it, with respect to the muscles; as to the nerves, the great sympathetic destined throughout to internal life, presents in the greater part of its branches an irregular distribution.
The solar plexus, the mesenteric, hypogastric, splenic, &c. afford examples of it.
We must then, I think, form this evident conclusion, that symmetry is the essential character of the organs of the animal life of man.
SECTION II.
Irregularity of external forms in organic life.
If we pass now to the viscera of organic life we shall see that a diametrically opposite character is applicable to them. In the digestive system the stomach, the intestines, the spleen, liver, &c. are all irregularly disposed.
In the circulatory system, the heart, the large vessels, such as the aorta, the venae cava?, the azygos, the vena porta, and the arteria innominata offer no trace of symmetry. In the vessels of the limbs, continual varieties are observed, and what is remarkable, in these varieties the disposition of one side, never affects that of the other.
The organs of respiration appear at first sight to be perfectly regular; if it is observed, however, that the right
bronchia differs from the left in length, diameter, and direction; that three lobes compose one of the lungs, and
C
