SURFACE AND SURGICAL ANATOMY. 
By HaARroup J. STILES. 
THE HEAD AND NECK. 
THE CRANIUM. 
Scalp.—The first and third layers of the scalp, namely, the skin and the 
occipito-frontalis muscle, are firmly united by fibrous processes which pass from the 
one to the other through the second or dense subcutaneous fatty layer. Inter- 
vening between these three layers and the pericranium is a loose cellular layer 
which supports the small vessels passing between the scalp proper and pericranium. 
The thin pericranium, although regarded anatomically as periosteum, possesses very 
limited bone-forming properties ; over the vertex it is readily separated from the 
skull-cap, except along the lnes of the sutures, where it gives off intersutural 
processes to join the endosteal layer of the dura. 
The free blood-supply of the scalp is for the purpose of nourishing its abundant 
hair follicles and glands. The main vessels he in the dense subcutaneous tissue, 
and are superficial, therefore, to the occipito-frontalis. The arteries supplying the 
frontal region are derived from the internal carotid, while those for the remainder 
of the scalp spring from the external carotid. These two sets of vessels anasto- 
mose freely with one another, and freely also across the mesial plane; hence the 
failure of ligature of the external carotid to cure cirsoid aneurysm of the temporal 
artery. 
Wounds of the scalp bleed freely, and the vessels are difficult to hgature on account of the 
adhesion of their walls within the septa of the dense subcutaneous tissue. In extensive flap wounds 
and in diffuse suppuration beneath the occipito-frontalis there is little danger of sloughing of the 
scalp. Abscesses and hemorrhages superticial to the occipito-frontalis are usually limited on 
account of the density of the subcutaneous tissue. Hemorrhage beneath the oceipito- -frontalis is 
seldom extensive on account of the small size of the vessels, Dut suppuration in this situation 
may rapidly undermine the whole muscle ; incisions to evac uate the pus should be made early, 
and parallel to the main vessels of the scalp. Extravasation of blood beneath the pericranium 
leads to a hzeematoma which is limited by the sutures. 
The veins of the scalp communicate with the intra-cranial venous sinuses— 
(1) directly through their anastomoses with the large emissary veins, namely, the 
parietal, which opens into the superior longitudinal sinus, and the mastoid and 
posterior condyloid, which open into the lateral sinus; (2) through the anastomoses 
of the frontal and supra-orbital veins with the ophthalmic vein, which opens into 
the cavernous sinus; (3) through the veins of the dipl6e, which connect the veins 
of the scalp and the pericranium on the one hand with those of the dura mater 
and the venous sinuses on the other; (4) through small veins which pass from the 
pericranium through the bones and the intersutural membranes to the dura. 
It is along these various channels that pyogenic infection may extend, from the 
scalp and pericranium, through the bone to the dura mater and venous sinuses, 
and from the latter to the cerebral veins, the pia-arachnoid, and the substance of 
the brain. More rarely the infection spreads from the cranial cavity along the 
emissary veins to the scalp. 
