LYMPHATIC DRAINAGE FROM THE TONSIL OF THE SOFT PALATE IN PIGS

The tonsil of the soft palate, the predominant lymphoid tissue of the oropharynx in pigs, is important especially in initiating immune respo nses against antigenic material entering the mouth. The aim of this wo rk was to describe the lymphatic pathways from the tonsils of the soft palate of pigs through lymph nodes of the head to the bloodstream. Th is was achieved by gross dissection, and by using Evans' Blue dye and Microfil casts. Efferent lymphatic vessels from the tonsil coalesce to form vessels which convey lymph to the primary nodes, the mandibular and medial retropharyngeal, and thence to the bloodstream, along two d istinct pathways. In the superficial pathway, lymph flows through the mandibular lymph node, along lymphatic vessels closely associated with the linguofacial vein, to the ventral superficial cervical node (midd le group) and the accessory mandibular node. Most efferent vessels fro m the accessory mandibular node enter the ventral superficial cervical node, but some may directly join the lymphatic vessels emanating from the ventral superficial cervical node. These vessels convey lymph to the dorsal superficial cervical node and thence, via the efferent lymp hatics, to the circulatory system. In the deep pathway, lymph is conve yed directly to the medial retropharyngeal node and then to the trache al trunk, as in other domestic animals. As the vessels from the tonsil s course over the surface of the pharynx, the muscular movements of sw allowing may help propel lymph towards the primary nodes and the blood stream.