| sheath of styloid process | A crest of bone (edge of the tympanic portion of the temporal bone) running from the front and medial side of the mastoid process to the spine of the sphenoid; it splits to ensheath the base of the styloid process. Synonym: vagina processus styloidei, vaginal process. (05 Mar 2000) |
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| sheath of thyroid gland | Covering of the thyroid gland external to its capsule formed by a splitting of the pretracheal layer of deep cervical fascia at the gland's posterior border; the anterior lamina covers the gland anterolaterally, attaching to the arch of the cricoid cartilage superior to the isthmus of the gland (causing it to move with the trachea during elevation/depression of the larynx); the posterior lamina passes posterior to the oesophagus to blend with the buccopharyngeal fascia; inferiorly, the sheath extends along the inferior thyroid veins to open into the superior mediastinum (hence, expansion of the thyroid, as by goiter, can take this direction). (05 Mar 2000) |
| sheath process of sphenoid bone | A thin lamina of bone that extends medially under the body of the sphenoid bone from the medial lamina of the pterygoid process; it articulates with the vomer and the palatine bone. Synonym: processus vaginalis ossis sphenoidalis, sheath process of sphenoid bone. (05 Mar 2000) |
| sheath rot | ulcerative posthitis |
| sheath-winged | <zoology> Having elytra, or wing cases, as a beetle. Source: Websters Dictionary (01 Mar 1998) |
| nerve sheath tumours | Tumours arising in the sheath surrounding the axon of some nerve cells and formed by the plasma membrane of schwann cells in the peripheral nervous sytem and by oligodendrocytes in the central nervous system. Neurofibromas and neurilemmomas are the most commonly occurring tumours of this type. (12 Dec 1998) |
| Neumann's sheath | A layer of tissue relatively resistant to the action of acids, which forms the walls of the dentinal tubules. Synonym: Neumann's sheath. (05 Mar 2000) |
| neurovascular sheath | Fibrous tissue enveloping and binding together arteries, their accompanying veins (venae comitantes) and nerves which run together; often it is merely the adventitious tissue of the neurovascular structures, but may be highly developed as a distinct fascial layer (e.g., in the case of the carotid or axillary sheaths). (05 Mar 2000) |
| notochordal sheath | The fibrous outer covering of the notochord. (05 Mar 2000) |
| Debye sheath | <radiobiology> The region of strong electric field in front of a material surface in contact with a plasma. Its characteristic thickness is the Debye length, and it is caused by Debye shielding of the negative surface charge resulting from electrons flowing to the surface much faster (initially) than the ions. The lost electrons leave behind a region of net positive charge which gradually diminishes the strength of the electric field over the Debye length. (13 Nov 1997) |
| dentinal sheath | A layer of tissue relatively resistant to the action of acids, which forms the walls of the dentinal tubules. Synonym: Neumann's sheath. (05 Mar 2000) |
| synovial sheath | See: synovial tendon sheath, vagina synovialis trochleae, synovial sheaths of digits of hand, synovial sheaths of digits of foot. (05 Mar 2000) |
| synovial tendon sheath | A sheath of synovial membrane enveloping certain of the tendons; it contains a small amount of synovial fluid. Synonym: vagina synovialis tendinis, mucous sheath of tendon, theca tendinis, vagina mucosa tendinis, vaginal synovial membrane. (05 Mar 2000) |
| dural sheath | An extension of the dura mater that ensheathes the roots of spinal nerves or, more particularly, the vagina externa nervi optici. (05 Mar 2000) |
| dural sheath of optic nerve | <anatomy, nerve> The outer sheath around the optic nerve, continuous with the dura mater. Synonym: vagina externa nervi optici, dural sheath of optic nerve. (05 Mar 2000) |