CELLULAR TISSUE.— Tela cellulosa, textus MUCOSUS) corpus,cribrosum, cellular mem brane, reticular membrane, filamentous, areolar, laminar tissue, &c. (Fr. tissu celluleux ; Germ. Zellgeweben.) The cellular tissue is the most universally diffused element of organization, and constitutes the basis of every animal body. It consists of a soft, areolated, and elastic sub stance. A somewhat similar structure also exists in vegetables, constituting their most simple or elementary texture.
In systematic works the cellular tissue is generally considered as a solid substance ; but as it really exists in the animal body, it is a compound of solid and fluid materials ; for in no part of any animal is the cellular membrane ever entirely devoid of fluid. This union of fluid and solid parts is indeed indispensable to organization, since there is no animal, or even vegetable, in which it may not be demonstrated. In the zoophyte the entire body appears to consist of the cellular tissue, and even in man it enters so largely into the formation of the different organs, pervading equally the most delicate and the most solid parts, that it con stitutes a species of mould of the whole body and of its individual parts ; indeed, if we ex cept the enamel of the teeth, and, as some authorities contend, also the nails, the hairs, and the epidermis, there is no solid in which it may not be detected.
Many anatomists have included the adipose tissue under the general denomination of cel lular membrane, but as the vesicles of the former are distinct from the cells of the latter, both as regards their formation and the riature of their contents, we rather incline to adopt the views of Malpighi, W. Hunter, Bedard, and others, who contend that the adipose and cellu lar tissues are distinct and separate structures.
(See ADIPOSE TISSUE.) Arrangernent.—The most striking and im portant fact relative to the cellular tissue is its uninterrupted continuity throughout the whole body, there being no part or region, however insulated it may appear to be, in which this communication may not be demonstrated. Whilst we fully admit this general communica tion, it is yet necessary to state that the cellular tissue may be appropriately divided into twd parts : the first division, called f'rom its dis position the common or interstitial portion (textus cellularis intermedius vel laxus), is that which occupies the spaces left between the various organs in all parts of the body ; the second division is distinguished by the name of the special cellular membrane (t. cellularis
strides, t. cellularis stipatzts), because it is proper to the several constituent parts of the body, investing each of them, and penetrating into their internal structure.
Of the C0111111011 cellular membrane.—It is in this division that the connection to which we have just referred is most free. Thus in the subcutaneous tissue placed between the skin and the fascirc of the muscles, there is an uni versal and evident communication. Again, in the head, the cellular membrane of the exter nal parts communicates with that of the internal through all the natural apertures--through the foramina of the base and other regions of the skull. From the face and cranium the con nexion may readily be traced to the neck, whence, after having pervaded all its parts, it passes in one direction behind the sternum and upper ribs to the thoracic cavity ; and in another underneath the clavicle and scapula on either side, to the arm-pit, which may be re garded as the common point of junction be tween the cellular substance of the neck, the trunk, and upper extremity.
The cellular tissue of the thorax is continuous with that of the abdomen through the openings of the diaphragm, and particularly beneath the sternum, around the aorta, the inferior vena cava, and the cesophagus. In a similar manner the connexion may be followed from the abdo men to the pelvis; from the former of these cavities under the crural arch to the inguinal region, which constitutes the point of union between the trunk and the lower extremity ; whilst from the pelvis the communication ex tends in one direction by the side of the rectum and urethra to the perineum, scrotum, and penis ; and in another by the obturator fora men and the ischiatic notch to the thigh.