Histology of the caprine hemal node.

Caprine hemal nodes were studied by light microscopy after glutaraldehyde fixation and epoxy resin embedding. A node consisted of a capsule, subcapsular and other sinuses, cortex, medulla and hilus. Elements of circulating blood filled the interstices of the reticular meshwork and associated macrophages which traversed the lumina of subcapsular and medullary sinuses. The latter were rare in 1-month-old goats, progressively increased in number and size in 2- to 4-month-old goats and coalesced with each other and the subcapsular sinus in adult animals. The cortical tissue appeared as lymphoid nodules. Circumferential lymphatic vessels abutted on outer margins of the nodules and gave origin to several radial lymphatics which branched and anastomosed between the medullary blood sinuses. Medullary cords were organized around the radial lymphatics. A single efferent lymphatic was formed at the hilum by confluence of the radial lymphatics. Our study, in contrast to earlier reports, shows that caprine hemal nodes possess efferent lymphatics. The present data suggest that the hemal nodes are involved, in addition to classical functions, in blood storage by hemoconcentration.