The greatest number of the fibrous aponeu roses are connected with muscular fibres, and in fact serve as tendons to them, and are de scribed as such. Of these we have the best examples in the fibrous aponeuroses of the ab dominal muscles, by which a considerable por tion of the paries of this cavity is constructed of a resisting inelastic material, which is at the same time under the control and regulation of muscular fibre. These expansions are corn posed of silvery white parallel fibres, in many places strengthened by bundles which cross and interlace with the fibres last named, e. g. the intercolumnar bands at the apex of the ex ternal abdominal ring. It is interesting to notice that in the larger quadrupeds, when the weight of the viscera is imposed on these aponeuroses, they are composed of the yellow elastic fibrous tissue. I have also seen the fascia lata thus converted.
A second class of these aponeuroses consists of those which cover the soft parts in particular regions. In general we find that where there are many muscles covered, the aponeurosis sends in processes by which each muscle is separately invested, these processes being ulti mately inserted into the periosteum of the bone. Thus the fascia lata of the thigh separates by means of processes prolonged from its deep surface, the various muscles to which it forms an external envelope, in such a manner that, if the muscles be carefully dissected away from a thigh, without opening the fascia more than is sufficient for their removal, it will appear to form a series of channels in which the muscles are lodged. A similar arrangement is found in the leg and foot, and in each of the segments of the upper extremity. The fascia lata has the peculiarity of being in a great degree influenced in its tension by a muscle, called from that office, tensor vagina femoris, and the fascia which covers the palm of the hand is likewise governed by the palmaris lava, the connec tion of which, however, with the fascia seems to have reference, not to the functions of the fascia, but to the power of the muscle, in aid of the other flexors of the wrist; the fasciae of the leg and arm too receive the terminal expan sion of the tendons of muscles. The strength of these aponeurotic sheaths is proportionate to the strength of the muscles they cover ; this is apparent, by comparing the fasciae of the arm and of the thigh; the strength of the latter greatly exceeds that of the former, and in the thigh itself the vastus extemus muscle is covered by a portion of the fascia lata, much stronger than those which cover the muscles on its posterior and inner aspects.
In a third class of aponeuroses are enume rated simple lamellae of fibrous membrane, which are found for the most part in connexion with the walls of cavities : such are the fascia transversalis, connected with the abdomen ; the fascia iliaca andpelvica, connected with the pelvis ; and the fibrous expansion lining the thorax, which has not received a name.
The aponeurotic fascim are most valuable in their power of resistance, and thus efficacious in maintaining organs in their proper situa tions; that they exert a considerable degree of compression upon the muscles is rendered evident by the hernia of the muscular fibres which takes place when an incision is made into the fascia lata of the thigh ; they thus re gulate the combined action of muscles and render more complete their isolated action. It is incumbent on the surgeon to remember how they confine purulent collections and oppose their progress to the surface, a property which is likewise observable in the cellular fascire, whose power of resistance is, however, much less, but their elasticity much greater.
Such is a brief notice of the generalities con nected with the fasciae of the body: the situa tion, connections, and structure of many of them are of great interest to the surgical anato mist, and will be found fully detailed in the articles devoted to the surgical anatomy of the regions. The subject is also very com prehensively treated in the following works, Godman, Anatomical Investigations, Phila. delph. 1824; l'elpean, Anat. Chirurgicale, t. i. ed. 2de ; Faillard, Description complete des Membranes fibreuses, Par. 1827 ; Cruveithier, Anat. Descript. t. ii. Aponeurologie, Par. 1834; Bourgcry, Anatomie de l'homme, t.
(R. B. Todd.) FAT. (cmcce, xi u n, adeps, pinguedo ; Fr. graisse; Germ. Fat; Ital.grasso.) Under this term we include a variety of animal pro ducts which bear a general resemblance to each other, and to a series of corresponding substances in the vegetable kingdom ; the fats of animals being, like the vegetable oils, ternary compounds of carbon, hydrogen, and oxygen, and not, apparently in any instance, containing nitrogen, except as an adventitious or acciden tal ingredient.