Persistent part of the envelope of Meckel's cartilage is:

Bone begins to develop lateral to Meckel cartilage during the seventh week and continues until the posterior aspect is covered with bone. Ossification stops at the point that will later become the mandibular lingula, and the remaining part of Meckel’s cartilage continues on its own to form the sphenomandibular ligament and the spinous process of the sphenoid. The part of Meckel’s cartilage that has been encapsulated with bone appears to have served its purpose as a splint for the intramembranous ossification, and it largely deteriorates. Key Concept: Persistent part of the envelope of Meckel’s cartilage is sphenomandibular ligament.