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followed by severe paralysis of the hand, but the use and power of the hand is regained in a few weeks; ablations, on the other hand, of even large portions of the 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 to the deeper part of the posterior wall of the central sulcus of Rolando. Anteriorly it extended into the pre-central sulci as well as into the occasional sulci which cross the anterior central gyrus ; indeed the hidden part of the motor area fully equals in


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Shows relations of the motor and sensory areas to the gyri, and to Chiene's lines.
G. Glabella.

C. Mid-point of AB. 0. External occipital protuberance (inion).

CD is drawn parallel to AM. M. Mid-point between G and 0.

Z. Post-auricular point. T. Mid-point between M and 0.

VW. Guide to anterior limit of transverse sinus. S. Mid-point between T and 0.

Y. Tympanic antrum. E. Zygomatic process of frontal.

X1. Site at which subarachnoid space may be opened. P: Root of zygoma (pre-auricular point).

X2 Site for draining lateral ventricle (Kocher). N. Mid-point of EP.

X3. Site for draining lateral ventricle (Keen). 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.

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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

Central blood-space



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Central blood-space 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 aineboid and often contain the debris of red blood corpuscles.

Arterial branches

enter at the hilum, run in the trabeculæ, and branch freely. The smaller mphoid sheath developed in their walls. This replaces the fibrous sheath which ies receive from the trabeculæ. Every here and there the lymphoid sheath trically or asymmetrically to form a lymphatic nodule (nodulus lymphaticus

of the nodules thus formed are quite small; others are visible to the naked eye , but, however large or small they may be, each contains a network of capillaries. termination the arteries lose their sheaths and become reduced to simple tubes of Is ; gaps appear in their walls and finally the cells forming them become conhe reticulum cells of the pulp. The veins begin in the same way as the arteries p is, therefore, the modified capillary system of the spleen. ent.—The spleen is mesodermal in origin. The first indication of its developmm. embryo, is a thickening of the dorsal mesogastrium. In 10-12 mm. embryos epithelium over the splenic rudiment is several layers thick. Soon the deeper thickening are transformed into mesenchyme and the epithelium is reduced again yer. The first vascularisation of the spleen is effected by a capillary network. Out ntra-splenic arteries and veins

The undifferentiated capileen them form capillary tufts 3. These become transformed alp. The exact method of this tion is undetermined, but during ss great numbers of red blood

Arterial branches roduced. The lymphatic nodules oped in the later part of fætal with their contained lymphocytes iate from the tunica adventitia of ies,

Accessory glomus



Accessory glomus -ne glomus coccygeum is a

body, 2-2:5 mm. in diameter, 1 immediately anterior to the tip e coccyx, upon a branch of the le sacral artery. Usually it is Entrance of artery

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Accessory.. es of similar structure and arterial

glomus tion.

Main glomus

Structure. — The glomus is enclosed Accessory

glomus a fibrous capsule and consists of round polyhedral cells with large nuclei lining considerable blood space, which is an nastomosing channel between an artery




ARTERY. (Reconstructed from serial sections through rom the capillary network of the region

the region.) From J. W. Thomson Walker. of the tip of the embryonic tail

. At first 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).





The first and third layers of the scalp, namely, the skin and the epiluscle, are firinly united by fibrous processes which pass from the one to : through the second or subcutaneous fatty layer. Intervening between ee layers and the pericranium is a loose cellular layer which supports the ssels passing between the scalp proper and pericranium. The thin peri, although regarded anatomically as periosteum, possesses very limited rming properties; over the vertex it is readily separated from the skull-cap, along the lines of the sutures, where it gives off intersutural processes to e endosteal layer of the dura. e free blood-supply of the scalp is for the purpose of nourishing its abundant ollicles and glands. The main vessels lie in the dense subcutaneous tissue, re superficial, therefore, to the epicranius (Fig. 1066). The arteries supplying rontal region are derived from the internal carotid, while those for the remainder e scalp spring from the external carotid. These two sets of vessels anastomose у with one another, and freely also across the median plane; hence the failure gature 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 esion of their walls to the dense subcutaneous tissue. In extensive flap wounds and in inse suppuration beneath the epicranius there is little danger of sloughing of the scalp. scesses and hæmorrhages superficial to the epicranius are usually limited on account of e density of the subcutaneous tissue. Hæmorrhage beneath the epicranius is seldom tensive on account of the small size of the vessels, but suppuration in this situation may apidly undermine the whole muscle and its aponeurosis-the galea aponeurotica ; incisions to vacuate the pus should be made early, and parallel to the main vessels of the scalp. Extravasa ion 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 diploe, 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.

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