TEXTURES.] ANATOMY 849 The endothelial lining of the Blood Vessels corresponds in general characters with that of the lymphatics. In the small blood capillaries the cells are fusiform ; in those of larger size, more irregular : in the veins they are broader, more irregular, and less distinctly fusiform than in the arteries. The endothelial covering of the endocardial lining of the heart consists of a layer of flattened cells with irregular outlines. The endothelial lining of the blood-vascular system is continuous with that of the lymph-vascular system, where the thoracic duct and other large lymph-vessels open into the great veins, and thus a continuity of surface is established between the serous membranes and the lining membrane of the blood-vascular system through the lymphatics. i The endothelium of the Synovial Membranes is formed of roundish, or polygonal, or tessellated cells, arranged after the manner of a stratified epithelium. Not unfrequently processes of the sub-endothelial vascular connective tissue covered by the endothelium project into the cavities of joints and synovial bursse. They have been called synovial fringes, and contribute to the formation of the synovia which lubricates the surfaces of a synovial membrane. The endothelium of the Cerebral Ventricles and Central Canal of the spinal cord is, as already stated, formed of spheroidal or cylindrical cells, possessing cilia on the free surface. The endothelial lining of the osseous labyrinth consists of flattened scales, whilst the membranous laby linth possesses a layer of polygonal cells. 3cZ Group. Cells imbedded in Solid Tissues. The cells which are imbedded in the solid tissues are either grouped together in considerable masses, or, as not unfrequently happens, are more or less separated by an intermediate matrix or intercellular substance. The matrix substance varies in its character in different tissues, and sometimes is so abundant as to obscure the cells. The textures which are constructed on this plan are of great importance, and constitute by far the larger propor tion of the tissues not only of the human body, but of the bodies of animals generally. Sometimes these tissues are elongated into delicate threads or fibres, at other times they are expanded into thin membranes, at others they form solid masses of considerable thickness. CONNECTIVE TISSUE. By the term connective tissue is meant a group of tissues which, though the members of the group differ in various respects from each other, both in naked eye and microscopic characters, yet agree in the property of binding or connecting together other tissues or parts of the body, and in serving as a supporting frame work for more delicate tissues. This group of tissues is the most extensively diffused of all the textures, for there is no organ in the body which does not contain one or other of its forms. The following varieties, based on modifica tions in their appearance and structure, may be recognised. a. Neuroglia. This name, which means nerve glue, has been applied by Virchow to the delicate tissue in the cen tral organs of the nervous system, and of the retina, which supports the nerve cells, nerve fibres, and blood-vessels of those parts. Mi croscopically it consists of small round or ovoid Fio. 35. Section of the white matter of the cerebrum mi- -flu, ncur0 gij ai nerve fibres, and capillary blood-vessels are represented. bedded in a Soft uudiffcrentiated protoplasm. A form of tumour, named Glioma, is sometimes produced by the excessive growth in the brain or retina of this variety of connective tissue. b. Retiform connective tissue constitutes the stroma or supporting framework of the lymphatic and other glanda which possess the adenoid type of tissue. It also forms the middle subdivision of the enamel organ of the teeth. It consists of stel late branching cells, the branches of which blend with each other, and form a delicate anastomosing FIG. so. Retiform connectives network or reticulum. In the H^e from a lymphatic gland. lymph glands, the colourless lymph corpuscles are set in the meshes of this network. In the solitary and Peyer s glands of the alimentary canal, in the tonsils, the back of the tongue, the posterior wall of the nasal part of the pharynx, the palpebral conjunctiva, the thymus gland, the pulp and Malpighian bodies of the spleen, colourless lymph-like corpuscles are also in eluded in the meshes of a reticulum. The name adenoid or lymphoid tissue is sometimes employed in describing this type of structure, and in some forms of disease the tissue increases in certain localities so largely FJQ- ST. Lymphoid ceils, included in n in mnnHrv o<j tr> fnrrn -nrnll rcticulnr mesh of connective tissue m quantity as tO lorm Well- f rom a lymphoid tumour of the defined lymphoid tumours. mediastinum. c. Gelatinous or mucous connective tissue (Schleimgewe bc ), forms the connective tissue of the embryo, the vitreous humour of the eye-ball, and the jelly of Wharton, which invests the blood-vessels of the umbilical cord. It is soft and jelly-like in consistency. Mi croscopically it consists of round ed, or spindle- like, or stellate cells, imbedded I a SOU tinOUS lular Substance. Sometimes the intercellular substance is in part differenti ated into short delicate fibres. Under some pathological conditions, this form of tissue increases largely in quantity in some parts of the body, and forms a kind of tumour named Myxoma. d. Fibrous connective tissue presents four modifications in appearance. It may be soft and delicate, with the fibres short and but faintly marked, as in the sub-epithelial tissue of the skin and mucous membranes. It may be loose, flocculent, and filamentous, and may contain small spaces or areolre (when it is called areolar tissue), which is well seen in the subcutaneous tissue of the adult, and in the omenta. It may be expanded in the form of a fibrous membrane, as in the fascite or aponeuroses, and the threads or fibres, strong and well marked, sometimes run parallel, sometimes cross each other at various angles. It may be collected into rounded or flattened bands, as in tendons and ligaments, where it forms the tendinous and ligamentous tissues. Here also the threads or fibres may be distinctly recognised and seen to run in parallel bundles, so as to I. 107 FIG. 38. Gelatinous connective tissue. The fusiform and intercel- stellate cells, and the partial differentiation into fibres
of the intercellular substance, are shown.
