Variation archive
The articles published on the portal, most recent first.
854 published articles
Variations in the muscles of the thumb have been reported to occur in one of every six subjects dissected. The most common variations occur in the long abductor and consist of an extensive cleavage of its tendon, or even the whole muscle, into separate parts. The belly of the muscle may be doubled. The long abductor may be reduced to a small slip arising only from the radius. The abductor pollicis longus may also arise from both the ulna and the mediolateral aspect of the radius.
This muscle is small and arises from the lateral tubercle of the calcaneus and inserts onto the tuberosity of the fifth metatarsal bone. Reference Wood, J. (1864) On some varieties in human myology. Proc. Roy. Soc. Lond. B 13:299-303.
This is a rare muscle that arises from the lateral process of the tuber calcanei and inserts onto the lateral surface of the base of the proximal phalanx of the little toe. See m. abductor digiti minimi (pedis).
Radiographs of the dorsal spine of a 3 year old female, showing absence of the posterior arches of D4-D7 (T4-T7), with marked widening of the spinal canal and multiple hemivertebrae involving the bodies of D6, 7 and 8 (T6-T8). Courtesy of Dr. Rafic Melhem, Dept. of Radiology, American University of Beirut, Beirut, Lebanon, May, 1980.
The usual grouping formula of 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal vertebrae is found in only about 20% of individuals studied. The cervical region is reported to be the most constant, the coccygeal the most variable. The number of elements of the vertebral column has been reported to vary between 32 and 35. Addition to a group is frequently seen, which occurs through the reduction in number of vertebrae of an adjacent group, the total number being unchanged. In this variation, the vertebra added is usually intermediate in form between the adjacent groups.
The body of the first thoracic vertebra may bear, on one or both sides, two costal pits resembling the usual thoracic type. The articulation of the head of the first rib is completed by a costal pit on the body of the seventh cervical vertebra. In rare cases the first thoracic rib may be rudimentary and similar in appearance to cervical ribs. The body of the second thoracic vertebra usually exhibits an identifying tubercle marking the attachment of a fasciculus of the medial portion of the longus colli muscle (Krmpotic).
The inferior margin of the vomer has been found in the intermaxillary suture, participating with the palatine bones in the formation of the hard palate. The vomer may be separated from the perpendicular plate of the ethmoid by a strip of cartilage from the nasal septum. The vomer may be fenestrated.
Eggemann and Inke (1963) cited by Lang (1983) reported that the greatest depth of the Sella Turcica was 8 mm with a range of 4 to 12 mm. The average depth was 6.85 mmin Europids; 7.03 mm in Mongolids, and 6.93 mm in Nigrids. The average length of the sella is 10.5 mm and a range of 5 - 16 mm and an average width of 14.0 mm and a range of 10 - 16 mm. The Sellar spine was first described by Lang (1977). The bony spine was 4.35 mm long and protruded from the dorsal side of the pituitary fossa into the fossa itself .
The number of ribs may be increased by addition at either the cervical or lumbar end of the series. It is extremely rare to find an additional rib or pair of ribs in both the cervical and lumbar regions at the same time. Eight true ribs have been observed. The first rib may be shorter than usual, slender and connected with the second costal cartilage. The number of ribs may also be decreased. The first rib is occasionally absent. It may be absent on one (or both sides) and shortened or hypoplastic on the other side.
Studies (see references) have shown that the stapes exhibits show marked variations. The head diffcrs in the prominence of its margins, shape of the articular facet and degree of inclination in relation to crural arches. No correlation can be made between the length of the stapcs and its weight. There may be a better relationship between breadth and weight of the ossicle. In the majority of cases, the posterior crus was found to be thicker, larger, and more curved than the anterior crus.
The first lumbar, instead of the twelfth thoracic vertebra, may present the transitional form of articular process. A lumbar rib may be present, united with the ventral surface of the transverse process or the tip of a short transverse process. The accessory rib may be elongated but is usually rudimentary. Lumbar ribs are less important clinically than cervical ribs and are usually mere rudiments An extra levator costae muscle is associated with a lumbar rib. In 559 skeletons of the Washington University collection, 8.8% had lumbar ribs (Lanier, 1944).
The number of vertebrae in the sacrum may be increased by fusion of the first coccygeal, by (less often) addition of the last (fifth) lumbar, or by addition of both the last lumbar and first coccygeal vertebrae. The number may be reduced to four by the "lumbarization" of the first sacral vertebra. In one study of 631 bodies, the sacrum was composed of five vertebrae in 77%, six in 21.7%, four in 1%, and seven in 0.2%.
References: Takata, G. (1922) On the value of bones as diagnostic material of fetal age. Folia Rnat. Japon. l(l):63-68.
According to Lang (1991) Blumenbach called sutural bones "gusset bones" because they are often situated like "patches" stitched into place between actual sutural lines. It is incorrect to call these wormian bones (for the description by Ole Worm (1588-1654), the anatomist), having been described about 100 years earlier by Paracelsus (Lang, 1991). Nearly 40% of skulls have sutural bones in the vicinity of the lambdoidsuture. Frequencies as high as 90% have been reported. Berry found sutural bones in 19th century Londoners in the vicinity of the lambda in 28.7% of men and 17.1% of women.
In a study of 433 knee joints, the menisci were found to be "C"-shaped in 422, discoid in nine, and circular in two. The medial meniscus may not be "C"-shaped but rather a ring completed by a ligament. In 140 knees, a menicofemoral ligament was present in 99 (71%). In 50 cases (36%) the ligament was the anterior meniscofemoral and in the remaining 49 cases (35%) it was the posterior meniscofemoral ligament. In 17 cases (12%) the anterior ligament was bilateral, in 12 cases (8%) the posterior was bilateral, and in two cadavers both ligaments were found in both knees.