Archive image from page 1388 of Cunningham's Text-book of anatomy (1914). Cunningham's Text-book of anatomy cunninghamstextb00cunn Year: 1914 ( GLOMUS COCCYGEUM. 1355 The arteries enter at tlie hilus, run in the trabecule, 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 trabeculse. 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
Archive image from page 1388 of Cunningham's Text-book of anatomy (1914). Cunningham's Text-book of anatomy cunninghamstextb00cunn Year: 1914 ( GLOMUS COCCYGEUM. 1355 The arteries enter at tlie hilus, run in the trabecule, 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 trabeculse. 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 con- tinuous 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 develop- ment, in a 9-mm. embryo, is a thickening of the dorsal mesogastrium. In 10-12 mm. embryos the ccelomic 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 capil- laries 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 fcetal life, and with their contained lymjmocytes differentiate from the tunica adventiti
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