LYMPH PATHWAYS OF THE MEDIAL RETROPHARYNGEAL LYMPH-NODE IN DOGS

In dogs, lymph drains from tissues throughout the head, including the tonsils, along lymphatic vessels to the I facial, parotid, lateral ret ropharyngeal and mandibular lymph nodes. From the mandibular lymph nod es, lymph may flow to the ipsilateral medial retropharyngeal lymph nod es; or along anastomotic connections to the contralateral node. Affere nt lymphatics convey lymph from these nodes to defined areas in the me dial retropharyngeal nodes. They divide over the surface of the node, and within trabeculae. Terminal afferent lymphatics are connected to t he subcapsular and trabecular sinuses either through circular oy oval holes in the vessel wall, or terminate at the sinus where the vessel c ontains a valve adjacent to the point of entry. The subcapsular sinus surrounds the entire node, and is continuous with an interconnecting n etwork of trabecular and cortical sinuses which convey lymph through t he cortex. Connective tissue septa extend through the sinuses and lymp h flows freely between adjacent sinuses through holes in the septal wa lls. Initial efferent lymphatic vessels, which arise from the medullar y sinuses between medullary cords, converge towards and unite within t he network of medullary trabeculae. Other vessels, which contain;valve -like flaps, drain lymph from the subcapsular sinus. Efferent vessels emerge along the hilus and coalesce to form the tracheal trunk. The tr acheal trunk has several layers of smooth muscle cells, well developed elastic laminae and connective tissue, surrounding the lymphatic endo thelium.