The attraction of cohesion in the parts of muscle appears to be
strongest in the direction of the fibres, and to be double that of the
contrary or transverse direction. When muscles cease to be irritable,
this attraction in the direction of the fibres is diminished; but it re-
mains unaltered in the transverse direction.
When muscles act more powerfully or more rapidly than is pro- portionate to the strength of the sustaining parts, they do not usually rupture their fleshy fibres, but generally break their tendons, or even an intmening bone; whence it is inferred, that the attraction of cohesion is more active and powerful in the contracted state of the muscle than during its relaxed or passive state.
The muscular parts of different classes of animals vary materially in colour and texture; and such variations occur not unfrequently in different parts of the same individual.
Sect. 2. Of the anatomical structure of muscles, and their relations with other parts of the animal hody.—The lecturer in this section professes to give no more than a rapid sketch of the history of muscular struc- ture. One example of the origin of a muscle he deduces from the process of the incubated egg: but here it remains doubtful whether the rudiments of the punctum saliens be part of the cicatrieula or- ganized by the parent, or merely a structure resulting from the first process of incubation. The anatomical structure of muscular fibres, he next observes, is generally complex, according as they are con- nected with membrane, blood-vessels, nerves, and lymphaeducts; which seem to be only appendages of convenience to the essential matter of muscle.
A muscular fibre, being carefully inspected in a powerful micro- scope, is found to be a solid cylinder, the covering of which, as had already been intimated in a previous part of the lecture, is a reticu— lar membrane, and the contained part a pulpy substance, irregularly granulated, and of scarce any cohesive power when dead.
The arteries articulate copiously upon the reticular coat of the muscular fibre; they anastomose with corresponding veins; but this continued canal is not supposed to act in a direct manner upon the matter of muscle. In what manner the capillary arteries terminating in the muscular fibre may effect all the changes of increase in the bulk or number of fibres, in the replenishment of exhausted mate- rials, and in the repair of injuries, is as yet matter of conjecture: but these arteries, it is thought, must be secretory vessels for de- positing the muscular matter, the lymphaeducts serving to remove the superfluous fluids and the decayed substances which are unfit for use. These lymphaeducts appear to receive the fluids they contain. not, as has been represented, from the projecting open ends of tubes, but from the interstitial spaces formed by the reticular or cellular membrane.
The functions of nerves in the muscular system are the next object of contemplation. These also, it seems, terminate in the reticular or cellular membrane, the common integument, and the connecting medium of all the dissimilar parts of an animal. We have to regret
