a. External Nose
Most of the lymph vessels of the external nose (Figure 13: 11) drain to the mandibular lymph nodes (Figure 13: 2, 2’), while a small number drain to the parotid lymph node (Figure 13: 1). They merge to form 3 to 6 larger lymph vessels, most of which pass under the muscles located in the lateral nasal region, though a few may run over these muscles, and then under the M. zygomaticus to the oral side of the masseter. From here, either all the lymph vessels (1 case) or most of the lymph vessels (2 cases) drain to the mandibular lymph nodes. One to 2 of the lymph vessels may turn across the M. masseter to drain to the parotid lymph node instead.
b. Nasal Cavity
The lymph vessels of the nasal cavity (nasal septum and turbinates) form beautiful, richly developed networks in the mucosa and submucosa, respectively.
The lymph vessels arising from these networks in the rostral half of the nasal cavity merge to form several lymph vessels, which leave the nasal cavity through the osseous nasal aperture, travel around the nasal process of the incisive bone, and then run outward to join the lymph vessels of the external nose and drain to the mandibular lymph nodes. In 6 more closely examined cases, none of the lymph vessels drained into the parotid lymph node (in contrast to the cow).
The lymph vessels in the caudal half of the nasal cavity, on the other hand, drain into the medial retropharyngeal lymph node. They leave the nasal cavity on each side through their respective choana as 2 to 3 larger vessels and travel caudally at the base of the skull, covered only by the mucous membrane of the pharynx, to drain to the medial retropharyngeal lymph node.
Lymph vessels from the middle part of the nasal cavity usually drain both rostrally and caudally.