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 responses against antigenic material entering the mouth. The aim of this work was to describe the lymphatic pathways from the tonsils of the soft palate of pigs through lymph nodes of the head to the bloodstream. This 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 distinct 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 (middle group) and the accessory mandibular node. Most efferent vessels from 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 lymphatics, to the circulatory system. In the deep pathway, lymph is conveyed directly to the medial retropharyngeal node and then to the tracheal trunk, as in other domestic animals. As the vessels from the tonsils course over the surface of the pharynx, the muscular movements of swallowing may help propel lymph towards the primary nodes and the bloodstream.