lacteals which are copiously ramified on every portion, particularly of the small intestines. This feature, however, will be better understood by inspecting the wood-cut on page 163, representing a portion of the bowel II, as attached to the spines by the mesentery MM, along which the absorbent vessels or lacteals LL are seen to pass from the gut towards the thoracic duct TD. The portion of peritoneum by which the small intestines are fixed to the spine, constitutes what is properly called the _mesentery_. That portion by which the larger bowel is attached is called the _mesocolon_, from its enclosing the colon; but in other respects the membrane presents no difference. The _muscular_ coat is composed principally of transverse and longitudinal fibres, and its sole object here, as elsewhere, is to effect _motion_. By the alternate contraction of the two kinds of fibres, the contents of the gut are gradually propelled in a downward direction, just as we see a motion propagated from one end of a worm to the other; and hence it is sometimes called the _vermicular or worm-like motion_ (from _vermis_, a worm). Some nauseating substances, such as emetics, have the power of _inverting_ the order of the muscular contractions, and directing the contents upwards instead of downwards--whence vomiting ultimately arises. Other substances, again, have the property of exciting the _natural_ action to a higher degree, and consequently propelling the contents faster downwards--in other words, of purging. Rhubarb, aloes, and similar laxatives, especially when combined with tonics, act in this way, and are consequently best adapted for obviating the kind of costiveness which arises from imperfect intestinal contraction. In a natural mode of life, the muscular coat is greatly aided in its operation by the large abdominal and thoracic muscles, brought powerfully and frequently into play during active exercise and employments. When this aid is withdrawn, as it is in sedentary people, the intestinal action often proves insufficient for the purpose; and hence the costiveness which is so invariable an attendant on most females, literary men, and others, whose occupations deprive them of active muscular exercise in the open air. In females, the use of tight stays renders the free expansion of the chest and corresponding motion of the abdomen, altogether impossible, and thus aggravates the evils of their sedentary mode of life. Hence also the peculiar fitness, in such cases, of the class of purgatives above alluded to, in preference to those of a saline nature, which act chiefly by stimulating the mucous surface to farther secretion.