ANIMAL TISSUES. 15 



treat of the entire animal kingdom, it occurs only partially. Other 

 tissues, which ordinarily receive special notification, may be re- 

 duced to one or other of the foregoing. Tendinous Tissue belongs 

 to Conjunctive Tissue, as does that of Skin proper (corium) : to this 

 also belongs in part Mucous Tissue (in the intestinal canal, &c.) 

 The Serous Membranes merit a special mention. They serve to 

 line cavities in the interior of the body, and ordinarily form sacs 

 which are closed on every side. They, too, belong to Conjunctive 

 Tissue, and are smooth only on their free surface, which is covered 

 with an epithelium. This smooth surface secretes a serous fluid. 

 We cannot admit a proper Glandular Tissue (tela glandulosa), as 

 most authors do. Under the term Gland Anatomists arrange very 

 different parts, of which the consideration belongs to special and 

 descriptive Anatomy. Lymph-glands (glandules lymphatics s. con- 

 globatce) which are found only in higher animals, are round or 

 oblong bodies of different size, in which one or more lymphatics are 

 distributed; these tortuous branches are again collected into larger 

 vessels, which pass out on the opposite side of the gland, to pursue 

 their course onward: numerous blood-vessels, whose fineness ex- 

 ceeds that of the lymphatics, surround all these branches. Conse- 

 quently lymph-glands are only vascular networks, and may be put 

 on a level with the so-called Eetia Mirabilia of the blood-vessels. 

 In the class of Glands, moreover, are reckoned different parts of 

 the animal body which, apart from their coverings, consist of con- 

 junctive tissue, blood-vessels and nerves, and for the most part have 

 an internal closed cavity which is filled with a granular fluid. 

 Such are the Supra-renal Capsules, the Thyroid gland, the Spleen, 

 the Thymus gland. These are the parts which HEUSINGER com- 

 prises under the name of parenchymatous tissue under which, 

 however, he also classes other parts, as the Lymphatics and the 

 Ovaries. Other authors style these parts Blood-glands (ganglia 

 sanguineo-vasculosa) , comparing them with the lymph-glands (gan- 

 glia lymphatico-vasculosd) ; but since these parts are not distin- 

 guished from others by their blood-vessels, the comparison is arbi- 

 trary. Finally, in a more special manner, the term gland is applied 

 to those parts of the animal body which secrete a fluid that does not 

 return into the current of the blood. These, in addition to lym- 

 phatics blood-vessels nerves and conjunctive tissue, have an efferent 

 canal (ductus excretorius} formed of mucous membrane, for the 



