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Show 210 DR. n. G A D O W O N T H E EVOLUTION [Mar. 18, of the upper lamina of the frontal bone, whjch forms the pedicle. This is a direct continuation of the frontal, identical with it in its dense, lamellar structure, numerous Haversian canals and its blood-supply, and it is covered by the same unaltered skin. It is, in fact, an exostosis or apophysial growth. On the apex of this pedicle the skin and the periost are thickened. The skin is devoid of sudoriferous glands, produces no stiff, but only very fine and soft, velvety hairs, is like them darkly pigmented and of a glabrous appearance. The cutis is in direct, intimate continuation with the periost, and contains numerous, but small vessels, chiefly lymphatic, and only capillaries perforate the periost. Immediately beneath it follows a dense layer of hyaline cartilage, which, together with rapidly proliferating connective tissue, makes up the apical portion of the pedicle and forms the growing point of the future pricket. Vertical sections through the growing pricket and pedicle show that the cartilage pervades the top portion in the shape of strands, trabeculae, and walls, which partition off equally proliferating masses of ingrowing connective tissue in which turn up bone-forming cells. The bulk of this ingrowing tissue comes in with the vessels which extend from the interior of the pedicle upwards into the base of the soft mass on the top; little connective tissue enters together with the small vessels of the periost. The process of ossification begins at the base and near the periost, pervading the whole growth in the shape of a very irregular framework, without forming concentric bone-lamellae and with but few Haversian canals. The first prickets or broaches are short-lived ; they are shed in the middle, or even earlier, of the first winter. The shedding of a full-grown antler has always lightly been referred to necrosis, but it is a rather complicated process. To begin with, the antler continues to ripen, or to harden, by the deposition of bone in the more spongy, axial centre, long after the velvet has been frayed off, the loss of which is consequently not the only, nor the main cause of the decay of the antler. The latter is nourished not only by the big vessels (branches of the temporal artery) which, ascending in the skin and periost, cause the " gutters," but also by the numerous vessels which ascend through the pedicle into the interior of the antler. The base of the latter, where it passes into the pedicle, becomes much denser and harder, instead of remaining somewhat spongy in the core, and the blood-supply is stopped. About the same time, at a level beloiv this junction, i. e. within the top portion of the pedicle itself, the Haversian canals are widened owing to activity of osteoclasts, and they become confluent into a " resorption-sinus." This is met by a ring-shaped furrow, which eats its way from the periost inwards. The hardened base of the antler is slightly convex, while the resorption- sinus forms a somewhat deeper cup on the top of the pedicle. Owing to this mode of resorption, which always affects the pedicle, this becomes lower every year, but it makes up for this loss by broadening. Long pedicles are consequently the older |
