True Tail Research Articles

Human tails and pseudotails

A case of a tail in a 2-week-old infant is reported, and findings from a review of 33 previously reported cases of true tails and pseudotails are summarized. The true, or persistent, vestigial tail of humans arises from the most distal remnant of the embryonic tail. It contains adipose and connective tissue, central bundles of striated muscle, blood vessels, and nerves and is covered by skin. Bone, cartilage, notochord, and spinal cord are lacking. The true tail arises by retention of structures found normally in fetal development. It may be as long as 13 cm, can move and contract, and occurs twice as often in males as in females. A true tail is easily removed surgically, without residual effects. It is rarely familial. Pseudotails are varied lesions having in common a lumbosacral protrusion and a superficial resemblance to persistent vestigial tails. The most frequent cause of a pseudotail in a series of ten cases obtained from the literature was an anomalous prolongation of the coccygeal vertebrae. Additional lesions included two lipomas, and one each of teratoma, chondromegaly , glioma, and a thin, elongated parasitic fetus.

The truncated normal–gamma mixture as a distribution for lead time demand

AbstractA central problem in inventory control concerns the statistical description of total demand during the lead time between placement and receipt of an order. Since both the demand per unit time and the lead time are random variables, the distribution of lead time demand is formulated as a mixture. In application, one or both components of the mixture are often assumed to be normally distributed despite their nonnegativity. In practice, this assumption is taken to imply that a normal curve, truncated at zero, is a valid description. Several approximations to the true tail area probabilities (given truncation) are examined. In turn, this leads to an improved and simpler expression for the normal–gamma mixture. Some numerical results are also presented.

II. Remarks on the Skeleton of the Archæopteryx; and on the Relations of the Bird to the Reptile

In Plate 1 of professor Owen's invaluable memoir on the Archæopteryx (Phil. Trans. 1863) the fifth vertebra behind the Acetabula is seized upon as the first of the caudal series. In Pl. 3, fig. 5, of the same memoir, we have the delineation of a young Ostrich’s pelvis; and in that figure the first post-femoral joint is marked as the commencement of the true tail; eight such joints being, even in the young bird, embraced by the posterior processes of the iliac bones.