 The retractor muscle envelopes the posterior end, and from the anterior portion of the mass proceed a number of ventro-lateral muscles, which unite with the immediately adjoining body-walls.The oesophagus enters the buccal cavity dorsally in the anterior fourth.The salivary glands are situate upon the posterior half of the buccal mass; they are fused together in the median line and partly envelope the oesophagus.