ANIMAL TISSUES. LS 
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 (coréwm): 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 (glandule lymphatice s. con- 
globate) 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 Retia 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-vasculosa) ; 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 
