The base of the cartilaginous portion of the Eustachian tube

Eustachian tube

The Eustachian tube is a tube that links the nasopharynx to the middle ear. It is a part of the middle ear. In adult humans the Eustachian tube is approximately 35 mm long. It is named after the sixteenth-century anatomist Bartolomeo Eustachi...

 (pharyngotympanic tube; auditory tube) lies directly under the mucous membrane

Mucous membrane

The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...

 of the nasal part of the pharynx, where it forms an elevation, the torus tubarius, the torus of the auditory tube, or cushion, behind the pharyngeal orifice of the tube. The torus tubarius is very close to the tubal tonsil

Tubal tonsil

The tubal tonsil is one of the four main tonsil groups which include the Palatine tonsil, the Lingual tonsil, the Pharyngeal tonsil, and the Tubal tonsil....

, which is sometimes also called the tonsil of (the) torus tubarius. Equating the torus with its tonsil however might be seen as incorrect or imprecise.

Two folds run inferiorly:

• posteriorly, the vertical fold of mucous membrane, the salpingopharyngeal fold
  Salpingopharyngeal fold
  A vertical fold of mucous membrane, the salpingopharyngeal fold, stretches from the lower part of the torus tubarius; it contains the Salpingopharyngeus muscle....
  
  , stretches from the lower part of the torus; it contains the Salpingopharyngeus muscle
  Salpingopharyngeus muscle
  The salpingopharyngeus muscle arises from the inferior part of the cartilage of the pharyngotympanic tube in the nasal cavity; it passes downward and blends with the posterior fasciculus of the palatopharyngeus muscle....
  
  .
• anteriorly, the second and smaller fold, the salpingopalatine fold
  Salpingopalatine fold
  In the lateral wall of the nasopharynx, the salpingopalatine fold, smaller than the salpingopharyngeal fold, stretches from the upper part of the torus tubarius to the palate anteroinferiorly; it contains the levator veli palatini muscle...
  
  , stretches from the upper part of the torus to the palate; it contains the levator veli palatini
  Levator veli palatini
  The levator veli palatini is the elevator muscle of the soft palate in the human body. During swallowing, it contracts, elevating the soft palate to help prevent food from entering the nasopharynx...
  
   muscle. The tensor veli palatini is lateral to the levator and does not contribute to the fold, since the origin is deep to the cartilaginous opening.