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llowed by severe paralysis of the hand, but the use and power of the hand is gained in a few weeks; ablations, on the other hand, of even large portions of he posterior central gyrus do not give rise even to transient paralysis.
In some of the animals experimented on, the motor area was found to extend > the deeper part of the posterior wall of the central sulcus of Rolando. Anteriorly extended into the pre-central sulci as well as into the occasional sulci which cross he anterior central gyrus; indeed the hidden part of the motor area fully equals in
FIG. 1067.-CRANIO-CEREBRAL TOPOGRAPHY.
Shows relations of the motor and sensory areas to the gyri, and to Chiene's lines.
0. External occipital protuberance (inion).
M. Mid-point between G and O.
T. Mid-point between M and O.
VW. Guide to anterior limit of transverse sinus.
S. Mid-point between T and O.
E. Zygomatic process of frontal.
P. Root of zygoma (pre-auricular point).
N. Mid-point of EP.
Site at which subarachnoid space may be opened.
R. Mid-point of PS.
extent that contributing to the free surface of the hemisphere. The motor areas extend a little in front of the superior and inferior pre-central sulci, which cannot therefore be regarded as physiological boundaries.
Reference to Fig. 1068 shows that, of the main areas, that for the lower extremity occupies the upper third of the motor region, that for the upper extremity the middle third, while the face occupies the inferior third. The relative topography of the chief subdivisions of these main areas is shown in Fig. 1069. It must be remembered, however, that there exists much overlapping of the adjacent areas.
The body of the lateral ventricle, which is equal in length to the posterior
tissue but includes many elastic and muscle fibres. From its deep surface, more especially at the hilum, strong trabeculæ pass into the organ to support the blood-vessels and nerves.
The pulp is a spongework of fine fibres covered, at places entirely concealed, by branched connective-tissue corpuscles, reticulum cells. Associated with these, occupying some of the
FIG. 1064.-SECTION THROUGH GLOMUS COCCYGEUM (highly magnified). From J. W. Thomson Walker.
smaller spaces of the spongework, are cells like very large leucocytes, spleen phagocytes. These are amoeboid and often contain the debris of red blood corpuscles.
The arteries enter at the hilum, run in the trabeculae, and branch freely. The smaller arteries have a lymphoid sheath developed in their walls. This replaces the fibrous sheath which the larger arteries receive from the trabeculae. Every here and there the lymphoid sheath expands symmetrically or asymmetrically to form a lymphatic nodule (nodulus lymphaticus lienalis). Many of the nodules thus formed are quite small; others are visible to the naked eye as white specks, but, however large or small they may be, each contains a network of capillaries. Towards their termination the arteries lose their sheaths and become reduced to simple tubes of endothelial cells; gaps appear in their walls and finally the cells forming them become continuous with the reticulum cells of the pulp. The veins begin in the same way as the arteries end. The pulp is, therefore, the modified capillary system of the spleen.
Development. The spleen is mesodermal in origin. The first indication of its development, in a 9-mm. embryo, is a thickening of the dorsal mesogastrium. In 10-12 mm. embryos the cœlomic epithelium over the splenic rudiment is several layers thick. Soon the deeper layers of the thickening are transformed into mesenchyme and the epithelium is reduced again to a single layer. The first vascularisation of the spleen is effected by a capillary network. Out of this the intra-splenic arteries and veins differentiate. The undifferentiated capillaries between them form capillary tufts or spherules. These become transformed into the pulp. The exact method of this transformation is undetermined, but during its progress great numbers of red blood cells are produced. The lymphatic nodules are developed in the later part of fœtal life, and with their contained lymphocytes differentiate from the tunica adventitia of the arteries.
(ii.) GLOMUS COCCYGEUM.
The glomus coccygeum is a small body, 2-25 mm. in diameter, placed immediately anterior to the tip of the coccyx, upon a branch of the
middle sacral artery. Usually it is Entrance of artery
Structure. The glomus is enclosed in a fibrous capsule and consists of round or polyhedral cells with large nuclei lining a considerable blood space, which is an anastomosing channel between an artery and a vein.
Development. The glomus develops from the capillary network of the region of the tip of the embryonic tail. At first
into main glomus
1065.-SCHEMA OF THE RELATION PRESENTED BY THE GLOMUS COCCYGEUM AND ITS ACCESSORY OUTLYING PARTS TO THE BRANCHES OF THE MIDDLE SACRAL ARTERY. (Reconstructed from serial sections through the region.) From J. W. Thomson Walker.
the capillary walls differentiate as if to form an artery, then the cells of the middle coat, instead of forming muscle, assume an epithelioid character.
The position of the glomus coccygeum at the posterior end of the axis of the body, and the fact that its blood-spaces form a wide arterio-venous anastomosis, suggest that it is a sort of safety-valve on the peripheral circulation. No evidence that it produces an internal secretion has, as yet, been obtained, and in spite of frequent statements to the contrary it contains no chromaphil cells (Stoerk).
SURFACE AND SURGICAL ANATOMY.
BY HAROLD J. STILES, F.R.C.S.
THE HEAD AND NECK.
Scalp. The first and third layers of the scalp, namely, the skin and the epicranius muscle, are firmly united by fibrous processes which pass from the one to the other through the second or subcutaneous fatty layer. Intervening 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 lines 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 lie in the dense subcutaneous tissue, and are superficial, therefore, to the epicranius (Fig. 1066). 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 anastomose freely with one another, and freely also across the median 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 ligature on account of the adhesion of their walls to the dense subcutaneous tissue. In extensive flap wounds and in diffuse suppuration beneath the epicranius there is little danger of sloughing of the scalp. Abscesses and hæmorrhages superficial to the epicranius are usually limited on account of the density of the subcutaneous tissue. Hæmorrhage beneath the epicranius is seldom extensive on account of the small size of the vessels, but suppuration in this situation may rapidly undermine the whole muscle and its aponeurosis-the galea aponeurotica; incisions to evacuate the pus should be made early, and parallel to the main vessels of the scalp. Extravasation of blood beneath the pericranium leads to a hæmatoma 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 sagittal sinus, and the mastoid and condyloid, which open into the transverse 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 diplöe, 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.
The lymph vessels of the anterior part of the scalp join the external maxillary lymph vessels; those of the temporal and parietal regions open into the pre-auricular and parotid lymph glands, situated in front of and below the ear, and into the post-auricular or mastoid glands, situated upon the insertion of the sterno-mastoid muscle. The lymph vessels of the occipital region open into the occipital glands, which lie close to the occipital artery where it becomes superficial in the scalp.