ssels and natural
arrest of haemorrhage--HAEMORRHAGE: _Varieties_;
_Prevention_; _Arrest_--Constitutional effects of
haemorrhage--Haemophilia--DISEASES OF BLOOD VESSELS:
Thrombosis; Embolism--Arteritis: _Varieties_;
Arterio-sclerosis--Thrombo-phlebitis--Phlebitis:
_Varieties_--VARIX--ANGIOMATA--Naevus: _Varieties_;
_Electrolysis_--Cirsoid aneurysm--ANEURYSM: _Varieties_;
_Methods of treatment_--ANEURYSMS OF INDIVIDUAL ARTERIES.

#Surgical Anatomy.#--An _artery_ has three coats: an internal coat--the
_tunica intima_--made up of a single layer of endothelial cells lining
the lumen; outside of this a layer of delicate connective tissue; and
still farther out a dense tissue composed of longitudinally arranged
elastic fibres--the internal elastic lamina. The tunica intima is easily
ruptured. The middle coat, or _tunica media_, consists of non-striped
muscular fibres, arranged for the most part concentrically round the
vessel. In this coat also there is a considerable proportion of elastic
tissue, especially in the larger vessels. The thickness of the vessel
wall depends chiefly on the development of the muscular coat. The
external coat, or _tunica externa_, is composed of fibrous tissue,
containing, especially in vessels of medium calibre, some yellow elastic
fibres in its deeper layers.

In most parts of the body the arteries lie in a sheath of connective
tissue, from which fine fibrous processes pass to the tunica externa.
The connection, however, is not a close one, and the artery when divided
transversely is capable of retracting for a considerable distance within
its sheath. In some of the larger arteries the sheath assumes the form
of a definite membrane.

The arteries are nourished by small vessels--the _vasa vasorum_--which
ramify chiefly in the outer coat. They are also well supplied with
nerves, which regulate the size of the lumen by inducing contraction or
relaxation of the muscular coat.

The _veins_ are constructed on the same general plan as the arteries,
the individual coats, however, being thinner. The inner coat is less
easily ruptured, and the middle coat contains a smaller proportion of
muscular tissue. In one important point veins differ structurally from
arteries--namely, in being provided with valves which prevent reflux of
the blood. These valves are composed of semilunar folds of the tunica
intima strengthened by an addition of connective tissue. Each valve
usual