sheath

sheath (sheth)

1. Any enveloping structure, such as the membranous covering of a muscle, nerve, or blood vessel. any sheathlike structure.vagina (1) ; 2. The prepuce of male animals, especially of the horse. 3. A specially designed tubular instrument through which special obturators or cutting instruments can be passed, or through which blood clots, tissue fragments, calculi, etc. can be evacuated. 4. A tube used as an orthodontic appliance, usually on molars. [A.S. scaeth]
axillary s.fibrous neurovascular s., formed as an extension of the prevertebral layer of deep cervical fascia through the cervicoaxillary canal, which enclosed the first part of the axillary artery, the axillary vein, and the brachial plexus.
carotid s.the dense fibrous investment of the carotid artery, internal jugular vein, and vagus nerve on each side of the neck, deep to the sternocleidomastoid muscle; the layers of cervical fascia blend with it.vagina carotica [NA] ;
caudal s.a group of microtubules arranged cylindrically around the caudal pole of the nucleus in a developing spermatozoon.
common flexor s.the synovial sheath that surrounds the eight tendons of the superficial and deep flexors of the digits of the hand as they pass through the carpal canal; it is commonly continuous with the digital sheath of the little finger.vagina communis musculorum flexorum [NA] , ulnar bursa;
common peroneal tendon s.the sheath that surrounds the tendons of the peroneus longus and brevis muscles in their passage across the ankle.vagina tendinum musculorum peroneorum communis [NA] , vagina tendinum musculorum fibularium communis;
crural s.femoral s
dentinal s.a layer of tissue relatively resistant to the action of acids, which forms the walls of the dentinal tubules.Neumann's s;
dural s.an extension of the dura mater that ensheathes the roots of spinal nerves or, more particularly, the vagina externa nervi optici.
dural s. of optic nerveexternal s. of optic nerve
enamel rod s.organic covering of the individual enamel rod.
external s. of optic nervethe outer sheath around the optic nerve, continuous with the dura mater.vagina externa nervi optici [NA] , dural s. of optic nerve;
external root s. See root s.
s. of eyeballfascial s. of eyeball
fascial s.'s of extraocular musclesmuscular s.; the part of the orbital s. that envelops the extraocular muscles; it is thin posteriorly but becomes thicker where it is continuous with the bulbar sheath; the fascial s.'s of the four rectus muscles are connected by an intermuscular membrane.fascia muscularis musculorum bulbi [NA] , fascia of extraocular muscles, muscular fascia of extraocular muscle;
fascial s. of eyeballa condensation of connective tissue on the outer aspect of the sclera from which it is separated by a narrow cleftlike episcleral space; the sheath is attached to the sclera near the sclerocorneal junction and blends with the fascia of the extraocular muscles.vagina bulbi [NA] , capsula bulbi, eye capsule, fascia bulbi, s. of eyeball, Tenon's capsule, vagina oculi;
femoral s.the fascia enclosing the femoral vessels, formed by the transversalis fascia anteriorly and the iliac fascia posteriorly; two septa divide the s. into three compartments, the lateral of which contains the femoral artery and the femoral branch of the genitofemoral nerve, the middle the femoral vein, and the medial is the femoral canal.crural s., infundibuliform s;
fenestrated s.a s. with a window cut in the tip or lateral convexity, through which special cutting instruments can be passed.
fibrous s.'s See fibrous tendon s., fibrous digital s.'s of hand, fibrous digital s.'s of foot.
fibrous digital s.'s of footfibrous sheaths of the toes, the tubular fibrous layer enclosing the synovial sheath and the tendons of the long and short flexors of the toes and the flexor hallucis longus in the digits; they are composed of annular and cruciform parts.vaginae fibrosae digitorum pedis [NA] ;
fibrous digital s.'s of handfibrous sheaths of the digits of the hand, the tubular fibrous layers that enclose the synovial sheaths and the superficial and deep flexor tendons and the tendon of the flexor pollicis longus in their passage along their respective digits; they are composed of annular and cruciform parts.vaginae fibrosae digitorum manus [NA] ;
fibrous tendon s.fibrous sheath of a tendon.vagina fibrosa tendinis [NA] ;
Henle's s.endoneurium
Hertwig's s.the merged outer and inner epithelial layers of the enamel organ which extends beyond the region of the anatomical crown and initiates formation of dentin in the root of a developing tooth; it atrophies as the root is formed, and any of the cells that persist are called Malassez' epithelial rests.
Huxley's s.Huxley's layer
infundibuliform s.femoral s
internal s. of optic nervethe innermost sheath around the optic nerve, continuous with the leptomeninges (pia-arachnoid) and including a cerebrospinal fluid-filled intervaginal space, continuous with the subarachnoid space.vagina interna nervi optici [NA] ;
internal root s. See root s.
intertubercular s.the extension of the synovial membrane of the shoulder joint downward in the intertubercular groove to surround the tendon of the long head of the biceps.vagina intertubercularis;
s. of Key and Retziusendoneurium
Mauthner's s.axolemma
medullary s.myelin s
microfilarial s.the membrane surrounding the embryos of certain blood-borne microfilariae, such as Wuchereria, Brugia, and Loa of humans; thought to be derived from the vitelline membrane.
mitochondrial s.the spirally arranged mitochondria in the middle piece of a spermatozoon; may control movement of the tail.
mucous s. of tendonsynovial tendon s
myelin s.the lipoproteinaceous envelope in vertebrates surrounding most axons of more than 0.5-mum diameter; it consists of a double plasma membrane wound tightly around the axon in a variable number of turns, and supplied by oligodendroglia cells (in the brain and spinal cord) or Schwann cells (in peripheral nerves); unwound, the double membrane would appear as a sheetlike cell expansion that is empty of cytoplasm but for a few narrow cytoplasmic strands corresponding to apparent interruptions of the regular myelin structure, the incisures of Schmidt-Lanterman; the myelin s. of each axon is composed of a fairly regular longitudinal sequence of segments, each corresponding to the length of s. supplied by a single oligodendroglia or Schwann cell; in the short interval between each two neighboring segments, the nodes of Ranvier, the axon is unmyelinated even though enclosed by complex finger-like plasmatic expansions of the neighboring oligodendroglia or Schwann cells.medullary s;
Neumann's s.dentinal s
neurovascular s.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 s.'s).
notochordal s.the fibrous outer covering of the notochord.
parotid s.parotid fascia
plantar tendon s. of peroneus longus musclethe synovial sheath surrounding the tendon of the peroneus longus in its course across the sole of the foot.vagina tendinis musculi peronei longi plantaris [NA] ;
prostatic s.loose fibrous, partly vascular enclosure of the prostate and its dense (true) fibrous capsule; it is continuous inferiorly with the superior fascia of the urogenital diaphragm and posteriorly becomes part of the rectovesical septum; it contains the prostatic venous plexus.
rectus s.sheath of the rectus abdominis, formed by the aponeuroses of the three anterolateral muscles of the abdominal wall that split to enclose the rectus and fuse medially to form the linea alba; it consists of an anterior lamina and a posterior lamina, the latter being absent below the arcuate line. See also aponeurosis of external abdominal oblique muscle, aponeurosis of internal abdominal oblique muscle.vagina musculi recti abdominis [NA] ;
resectoscope s.an operative s. through which transurethral electroresection of bladder tumors or prostate gland can be performed.
root s.one of the epidermic layers of the hair follicle: external root s. is continuous with the stratum basale and stratum spinosum of the epidermis; internal root s. comprises the cuticle of the internal roots, Huxley's layer, and Henle's layer.
Rouget-Neumann s.the amorphous ground substance between an osteocyte and the lacunar or canalicular wall.
Scarpa's s.cremasteric fascia
s. of Schwannneurilemma
s. of Schweigger-Seidelellipsoid
s. of styloid processa 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.vagina processus styloidei [NA] , vaginal process;
synovial s. See synovial tendon s., vagina synovialis trochleae, synovial s.'s of digits of hand, synovial s.'s of digits of foot.
synovial s.'s of digits of footsimilar in structure to the corresponding sheaths of the hand.vaginae synoviales digitorum pedis [NA] ;
synovial s.'s of digits of handthe synovial sheaths that enclose the flexor tendons of the fingers and line the inside of the fibrous tendon sheaths. vaginae synoviales digitorum manus [NA] ;
synovial tendon s.a sheath of synovial membrane enveloping certain of the tendons; it contains a small amount of synovial fluid.vagina synovialis tendinis [NA] , mucous s. of tendon, theca tendinis, vagina mucosa tendinis, vaginal synovial membrane;
tail s.the protoplasmic envelope in the tail of a spermatozoon.
tendon s. of abductor pollicis longus and extensor pollicis brevis musclesthe synovial sheath lining the compartment of the extensor retinaculum that contains the abductor pollicis longus and extensor pollicis brevis tendons.vagina tendinum musculorum abductoris longi et extensoris brevis pollicis [NA] ;
tendon s. of extensor carpi radialis musclesthe synovial sheath lining the compartment of the extensor retinaculum containing the tendons of the extensor carpi radialis longus and brevis muscles.vagina tendinum musculorum extensorum carpi radialium [NA] ;
tendon s. of extensor carpi ulnaris musclethe synovial sheath surrounding the tendon of the extensor carpi ulnaris in its course deep to the extensor retinaculum.vagina tendinis musculi extensoris carpi ulnaris [NA] , peritenon;
tendon s. of extensor digiti minimi musclethe synovial sheath surrounding the tendon of the extensor digiti minimi in its passage deep to the extensor retinaculum.vagina tendinis musculi extensoris digiti minimi [NA] ;
tendon s. of extensor digitorum and extensor indicis musclesthe synovial sheath that surrounds the four tendons of the extensor digitorum muscle and the tendon of the extensor indicis deep to the extensor retinaculum.vagina tendinum musculorum extensoris digitorum et extensoris indicis [NA] ;
tendon s. of extensor digitorum longus muscle of footthe synovial sheath that surrounds the tendons of the extensor digitorum longus muscle and the peroneus tertius in their passage across the ankle.vagina tendinum musculi extensoris digitorum pedis longi [NA] ;
tendon s. of extensor hallucis longus musclethe synovial sheath that surrounds the tendon of the extensor hallucis longus in its passage across the ankle.vagina tendinis musculi extensoris hallucis longi [NA] ;
tendon s. of extensor pollicis longus musclethe synovial sheath surrounding the extensor pollicis longus tendon in its passage deep to the extensor retinaculum.vagina tendinis musculi extensoris pollicis longi [NA] ;
tendon s. of flexor carpi radialis musclethe synovial sheath enclosing the tendon of the flexor carpi radialis as it crosses the wrist.vagina tendinis musculi flexoris carpi radialis [NA] ;
tendon s. of flexor digitorum longus muscle of footthe synovial sheath that envelops the flexor digitorum longus tendons as they pass into the foot deep to the flexor retinaculum.vagina tendinum musculi flexoris digitorum pedis longi [NA] ;
tendon s. of flexor hallucis longus musclethe synovial sheath that envelops the tendon of the flexor hallucis longus as it passes into the foot deep to the flexor retinaculum.vagina tendinis musculi flexoris hallucis longi [NA] ;
tendon s. of flexor pollicis longus musclethe synovial sheath that envelops the tendon of the flexor pollicis longus in its course through the carpal canal; it is continuous with the digital sheath of the thumb, the two generally being considered as one sheath.vagina tendinis musculi flexoris pollicis longi [NA] , radial bursa;
tendon s. of superior oblique musclethe synovial sheath enclosing the tendon of the superior oblique muscle as it passes through the trochlea.vagina tendinis musculi obliqui superioris [NA] , synovial trochlear bursa, trochlear synovial bursa, vagina synovialis trochleae;
tendon s. of tibialis anterior musclethe synovial sheath, deep to the extensor retinaculum, that surrounds the tendon of the tibialis anterior as it crosses the ankle.vagina tendinis musculi tibialis anterioris [NA] ;
tendon s. of tibialis posterior musclethe synovial sheath surrounding the tendon of the tibialis posterior as it passes into the foot deep to the flexor retinaculum.vagina tendinis musculi tibialis posterioris [NA] ;
s. of thyroid glandcovering 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 esophagus 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).
vascular s.'sfibrous envelopes ensheathing the arteries with their accompanying veins and sometimes nerves as well.s.'s of vessels, vaginae vasorum;
s.'s of vesselsvascular s.'s
Waldeyer's s.the tubular space between the bladder wall and the intramural portion of the ureter as it courses obliquely through this structure; actually a space and not a true s.Waldeyer's space;

 

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