854 published articles
This muscle is obviously larger in the male. Some of the more anterior fiber bundles may extend to the dorsal surface of the penis and form a pubocavernosus (or levator penis) muscle. A compressor venae dorsalis has been described, composed of a few fascicles that arise from the sheath of the corpus cavernosum urethrae and from the median raphe, and unite with those of the opposite side by a tendon that passes over the dorsal vein.
The interossei are occasionally doubled in one or more spaces or they may be absent in one or more spaces. The palmar interossei insert into the extensor expansion. The first dorsal interosseous muscle inserts into the extensor expansion. The first dorsal interosseous muscle usually inserts into the the proximal phalanx. The three other dorsal interossei are variable. Most frequently they insert into the extensor expansion and the proximal phalanx. The second dorsal interosseus inserts into the proximal phalanx more frequently than the fourth, and the fourth more frequently than the third.
Infraspinatus is sometimes inseparably united with teres minor. Infrasinatus minor is a superior fascicle that is distinctly separated from the main muscle mass. Infraspinatus superficialis is a fascicle extending from the border of the spine of the scapula to the greater tuberosity of the humerus. A slip connecting this muscle with the posterior border of the deltoid (see m. deltoideus) has also been described (Henle). Syn.: m. Untergrätenmuskel, Sous-èpineaux.
The psoas and iliacus muscles are occasionally completely independent muscles. The psoas may be divided longitudinally into fascicles. An accessory slip has been described lateral to the muscle and separated from it by the femoral nerve. Iliacus may be pierced by the femoral nerve. Mori reports that the psoas major arose from the first lumbar vertebra in 98.6 % of his 152 sides (76 cadavers), and from the second lumbar on two sides, 1.3%. In no instance did the muscle arise from thoracic vertebrae.
Fibers arising from the the lesser cornu of the hyoid bone and inserting on the dorsum of the tongue are frequently separate from the hyoglossus and have been named chondroglossus. The fibers arising from the body of the hyoid are frequently separated by a distinct interval from those arising from the greater cornu, the former constituting the basioglossus and the latter, the ceratoglossus. A bundle of fibers, forming triticeoglossus, arise from the cartilago triticea, passing proximally and forward to insert along with the posterior fibers of the hyoglossus.
Occasionaly, the gracilis supplies fibers to the fascia lata and to the fascia of the leg. A gracilis biceps has been reported with a normal upper head and a lower head arising from the ramus of the ischium. Syn: m. rectus internus, Schlanker Schenkelmuskel, Droit interne.
Detached slips may connect the muscle with the tensor fasciae latae, superior gemellus, upper part of the origin of the vastus lateralis, or the capsule of the hip joint. This last form may appear as an accessory muscle under cover of the main mass. The anterior and posterior parts may be separate, or the anterior fibers may detach from the rest and form an independent muscle, the gluteus quartus. Gluteus quartus may be homologus to invertor femoris of apes. Syn.: m. gluteus minor s. tertius, Kleiner Gefässmuskel, petit fessier.
This muscle may be divided into two lamallae, or the deeper fibers may end on a separate tendon that inserts into the upper border of the greater trochanter. The muscle may supply slips that join the tendon of piriformis. A gluteus medius accessorius has been described as arising from the iliac crest under tensor fasciae latae and gluteus medius and inserting on the greater trochanter, partly with medius and partly independently. Gluteus quartus (gluteus scansorius) is a rare muscle arising between gluteus medius and minimus and inserting onto the tip of the greater trochanter.
Variations are rare. The most medial fibers may separate to insert on the lateral lip of the linea alba. The muscle may receive an additional fasciculus of origin from the lumbar aponeurosis or ischial tuberosity. This fasciculus may be independent (ischiofemoral muscle). A distinct slip (coccygeofemoral) at the lower border of gluteus maximus, arises from the coccyx and attaches to the femur, is also found and represents a caudal head.
The genioglossus may send a slip to the epiglottis, levator epiglottidis . It may send some fibers to the superior constrictor of the pharynx (geniopharyngeus) or to the stylohyoid ligament. Parts of the muscle may become isolated; for instance, a fasciculus might extend from the mental spine to the tip of the tongue (longitudinalis linguae inferior medius) .
The gemelli vary in size. The superior gemelus may be small or absent, or may be doubled and may insert into the capsule of the hip joint. The inferior gemellus may also be doubled; its absence has also been reported but more rarely than the superior muscle. Terry reported that the superior gemellus was absent, on one side or both, in 31 of 254 cadavers. Wood reported the superior gemellus was absent in 4 of 70 bodies, three male and one female. Nakano found no gemelli absent, in Chinese bodies, in 75 body halves.
In view of its phylogenetic history and its development in humans, the gastrocnemius has been considered a muscle of the fibular side of the leg. This may also be true of the lateral head of the soleus. The soleus appears first in lower mammals and may be a derivative of the lateral head of the gastrocnemius. It has been suggested that the medial head of gastrocnemius is medial extension from the fibular head. The gastrocnemius is frequently joined by a separate fascicle or head known as the third head of gastrocnemius. It arises from some part of the popliteal surface of the femur.
Flexor pollicis longus is uniquely human. In other primates there is only one common deep flexor that provides a tendon to the thumb. In some cases, this condition is exactly duplicated in humans; in other cases, the muscle has been found fused with the index tendon of flexor digitorum profundus (as in the gorilla and chimpanzee). A deep accessory muscle was found, which bifurcated to join both flexor pollicis longus and flexor digitorum profundus (the tendon to flexor indicis).
The flexor pollicis brevis has been reported absent or incorporated into the opponens. The muscle may be inseparably joined to adductor pollicis. The belly of the muscle may be divided. The muscle may be doubled or absent. An interesting pattern of innervation has been reported for this muscle. The superficial head may be innervated by the median, ulnar or both nerves with a frequency ratio of 13-10-7, while the deep head is innervated primarily by the ulnar (16 of 24 cases), by the median (3 of 24 cases), or by both nerves (5 of 24 cases).
The connection between the tendon of the long flexor of the great toe and that of flexor digitorum longus is constant, but variable. A slip is commonly sent from the flexor hallucis to the flexor digitorum, but frequently an additional slip passes, in the reverse direction, from flexor digitorum to flexor hallucis. Complete division of the tendons is very rare.
The flexor brevis is often fused with the adductor. It may be covered by the abductor hallucis and short flexor of the toes. A slip (opponens hallucis), which is attached to the first metatarsal bone has been described. Sometimes this slip is separated from the rest of the muscle and is inserted on the length of the metatarsal shaft. Occasionally, another slip of muscle is observed arising from the cuneiform bone and joining the medial head of the muscle at its insertion. Flexor hallucis brevis occasionally sends a slip to the proximal phalanx of the second toe.
Some variations in this muscle have been termed retrogressive in that they represent remnants of the connections between two sheets of muscle. Thus, a slip very frequently connects superficialis with the long flexor of the thumb (flexor pollicis longus) or flexor digitorum profundus as muscular slips occasionally pass between superficialis and deep flexors of the fingers.
This muscle has a radial origin in about 84% of cases studied (Mori).The various ways the deep and superficial flexors may be united are discussed under m. flexor digitorum superficialis (sublimis). In addition, a connection with flexor digitorum superficialis and or flexor pollicis longus is frequent, generally in the form of a slip passing to the index finger tendon of the deep flexor. The number of bellies to the muscle may be increased. The origin of the belly to the index finger may not be limited to the radius but may reach the interosseus membrane.
The deep portion of this muscle may provide slips to a variable number of digital tendons of the long flexor, most commonly to those of the second, third, and fourth toes. The tendon to the second toe may be absent and replaced by a tendon from flexor hallucis longus. A slip is sometimes provided to the fifth toe, replacing the tendon from the short flexor. Another slip passes to the tendinous connection between the tendon of flexor hallucis longus and that of flexor digitorum longus.
The Slip from flexor brevis to the little toe may be defective or absent. It may be present but fail to reach the toe, ending in fascia. It may arise separately from the fibular band of the plantar aponuerosis. It is absent in about 21% of cases, but may be replaced by a small fusiform muscle arising from the long flexor tendon, with occasional additional attachments to the medial tubercle of the calcaneus, lateral intermuscular septum, or accessorius (quadratus plantae). The muscle or its tendons may be more or less joined to the tendons of flexor digitorum longus.
