854 published articles
In the great majority of cases, some of the deeper fibers end on the lateral border of the shaft of the fifth metatarsal bone. This part of the muscle is occasionally found as a separate and independent slip. Syn.: m. Flexor brevis digiti pedis quinti.
This muscle is extremely variable and is frequently united with, or replaced by, the abductor and sometimes by opponens digiti minimi. It may also be replaced by a tendinous band that arises from flexor carpi ulnaris and inserts onto the base of the fifth proximal phalanx and hook of the hamate. The muscle may be doubled and the absence of flexor digiti minimi brevis has been reported (Cloquet). Flexor brevis may be associated with an accessory palmaris slip joined to it. It was found with an unciform (os hamatum) origin alone. The muscle may send a slip to the head of the metacrpal bone.
In one case, the anterior fibers of this muscle formed an accessory muscle that joined the main belly below the middle of the forearm; it was supplied not by the ulnar but rather by the median nerve. Because its two heads are completely independent and usually supplied by the ulnar nerve, it has been suggested that the muscle is formed developmentally of two elements that fuse. It may however, remain doubled and not fuse. An additional slip of origin from the medial side of the coronoid process is often present.
At its origin, the flexor carpi radialis has been observed to receive an additional slip from the tendon of insertion of the biceps or its tendinous expansion, brachialis, the coronoid process of the ulna (~5%), or from the anterior oblique line of the radius. Its insertion is subject to frequent variations, the most common being partial or total attachment to the trapezium. It may also be partly inserted into the flexor retinaculum or navicular (scaphoid) bone, and a supplementary slip to the third metacarpal may be extended to the fourth.
Doubling of this muscle is frequent, and the ulnar portion may pass beneath the dorsal ligament with the common extensor. It has been reported the this muscle is absent in about 1.5% of individuals. Macalister reported the variations of this muscle as follows: 1. It may receive a slip of extensor digitorum communis which runs in the same in the radius (wood); 2. Macalister found the muscle doubled with both tendons inserting as usual; 3. Giving a slip to the base of the first phalanx in a case where extensor pollicis longus was absent; 4.
Extensor pollicis brevis, a muscle peculiar to (or individualized to a greater degree in) humans is sometimes absent, being fused with abductor longus, as in the Simiidae. On the other hand, its tendon is often united with that of the long extensor and is inserted with it, or it may be continued as an independent slip to the base of the distal phalanx. In a study of 118 forearms extensor pollicis brevis inserted onto the first phalanx in 72% of cases, both phalanges in 21%, and the terminal phalanx only, in 6.8%. Extensor pollicis brevis has been reported absent in 6.3% of cases.
The muscle of the index finger is rarely absent. The origin of the muscle may shift from the ulna to the radius, the carpus, or the interosseous membrane. Extensor indicis may blend with extensor secundii internodi pollicis (extensor pollicis longus). An unusual extensor indicis muscle has been found arising from the lunate, navicular (scaphoid) and capitate bones and terminating on the head of the proximal phalanx of the index finger. It may have two heads or the muscle may be completely doubled. Macalister reported the variatins of extensor indicis as follows; 1.
This muscle is occasionally united at its origin with extensor digitorum longus. The tendon may be divided into three slips confined to the great toe; a slip to the second toe has also been observed. Macalister found the following variations for this muscle: 1. The muscle may be doubled (Meckel, Henle); 2. It may have a common muscular slip between it and extensor digitorum; 3. With a slip to the extensor hallucis brevis at the junction of its muscle and tendon; 4. It may be joined to extensor ossis metatarsi hallucis.
Variations in this muscle relate mainly to the origin and arrangement of its various tendons. They may be doubled, or extra slips may arise from one or more tendons to their corresponding metatarsal bones, to the short extensor, or to one of the interosseous muscles. A slip to the great toe from the innermost tendon has also been seen. In contrast to the corresponding tendons in the hand, all are independent of their neighbors; their are no connecting bands between them.
Variations of extensor digitorum communis include the occasional deficiency of one or more tendons of insertion or an increase in their number to five, supplying the five digits. If one of the tendons is absent it is usually that to the fifth digit. More frequently, however, the tendons are limited to the index or middle finger alone, although an additional slip to the thumb is occasionally seen. Any digit may receive two tendons. Wood reported a hand with tendons doubled to the second, third and fifth fingers.
The short extensor of the toes is both ontogenetically and phylogenetically a fibular muscle. Its position on the dorsum of the foot is secondary. The muscle may have three distinct heads rather than the usual four. The medial and largest belly supplying the great toe is named extensor hallucis brevis. An accessory fasciculus originating from the talus and navicular bones or from the third cuneiform and third metatarsal bones has been found inserting into the second slip of extensor brevis and, as well, a fasciculus from the cuboid may join the third slip of extensor brevis.
A thin fibrous slip from the lateral epicondyle of the humerus and continuous with the common tendon is occasionally present. More rarely, there is a supplementary origin from the dorsal surface of the ulna. The belly of the muscle may be doubled. The tendon of insertion is sometimes divided and gives a slip to the fourth digit. An ulnar slip has been observed to end on the base of the fifth metacarpal, thus exactly reproducing the arrangement of the serially homologous slip known as peroneus tertius in the leg.
Extensor carpi ulnaris is the ulnar marginal element of the primitive extensor sheet and corresponds to the two peroneal muscles in the leg. Several variations are of interest in this connection: a) the muscle is occasionally doubled throughout, b) there may be a partial attachment of its tendon to the base of the third or fourth metacarpal bone, c) an additional tendon may replace an absent extensor digiti quinti, and d) an independent muscle ulnaris digiti minimi or ulnaris digiti quinti has been observed arising from the lower part of the dorsal surface of the ulna and inserting onto the ba…
In lower mammals the two extensores carpi radiales are represented by one muscle; human cases have been reported in which the two muscles were fused, the common belly having two or three tendons inserted into the metacarpal bones. A trigastric radialis longus has been reported inserting partially onto the base of the first metacarpal and partially onto the base of the second metacarpal. Incomplete fusion frequently occurs, effected by cross slips from one muscle to the other. The longus and brevis are noted for exchange of fleshy and tendinous slips.
Gruber reported a study of 200 elbow regions from 100 cadavers. He found this muscle in 26 males and 8 females. The muscle was found bilaterally in 15 male and 4 females and on one side only in 11 males and 4 females. It was on the right side only in 9 males and 3 females and on the left side alone in 2 males and 1 female. Wood reported the muscle in 4 male subjects out of 36. In three instances the muscle was bilateral, and in one on the left side only.
A close relationship exists between the posterior belly of digastricus and the stylohyoid. Both are also innervated by the facial nerve. One or the other may fail to separate from the common mass of mesenchyme, from which they are derived. A bundle of muscle fibers sometimes pass from the tip of the styloid process to the angle of the mandible, forming what may be termed stylomandibularis. The posterior belly of digastricus may originate from any part of the mastoid groove or even from the outer portion of the superior nuchal line. Occasionally, it fuses with the stylohyoid.
The anterior belly of the digastric is highly variable. Mori , having studied 262 cadavers, classified the into 7 types as follows: A close relationship exists between the mylohyoid and the anterior belly of the digastric. There is usually some exchange of fibers sometimes amounting to complete fusion of the two muscles. Doubling of the anterior belly is a rather common variation, and the anterior bellies of opposite sides may be united by conversion of the fascia that typically passes between them into muscular tissue.
The sternal portion of the diaphragm may be absent, and its costal origins may extend from the sixth or even the fifth rib. The slip from the twelfth rib may be absent; if this is associated with an absence of the fibers from the lateral arched band, the lumbocostal trigone becomes an extensive gap. This condition, in exaggerated form, occurs in congenital diaphragmatic hernia. In such cases, it may be noted that the lumbar portion of the diaphragm extends anteroposteriorly on the medial side of the aperture.
A bundle of muscle fibers may arise from the inferior border of the depressor and pass obliquely downward and inward toward the median line beneath the chin, either terminating in superficial fascia of that region or uniting with a counterpart from the opposite side. This slip is considered a distinct muscle, the transversus menti. The depressor may appear as three distinct fascicles. Syn.: m. depressor labii inferioris, triangularis.
This muscle arises from the lateral border and upper surface of the acromion, from the ventral and upper surface of the lateral part of the clavicle, and from the spine of the scapula. The clavicular and even the acromial part of this muscle may be missing. Rarely, the muscular sheet may be split into three main parts that are more or less separated from each other; the independence of the acromial part was reported by Macalister and by Mori.
