Location Of Ligaments Research Articles

Morphology of larvae of the family Mytilidae (Bivalvia) from the north-western part of the Sea of Japan

The larval shell morphology of 10 bivalve species of the family Mytilidae (Adula falcatoides,Crenella decussata,Crenomytilus grayanus,Modiolus kurilensis,Musculista senhousia,Mytilus coruscus,Mytilus galloprovincialis,Mytilus trossulusandSeptifer keenae, and an unidentified species Mytilidae indeterminate) from the Sea of Japan is described. The following morphological features were comparatively examined: larval shell outlines including shape and size of umbones, and anterior, posterior and ventral margins, hinge morphology, ligament location, sculpture, colour, and eye-spot outlines. Some dimensional parameters of larval shells are given. The time interval of occurrence of larvae in the plankton, water temperature in this period, and shell length of competent larvae are presented. It is demonstrated that, in spite of sometimes similar external morphological characters, identification of mytilid larvae creates no difficulties if all distinguishing characters are used.

Anatomy of the squirrel wrist: bones, ligaments, and muscles.

Anatomical differences among squirrels are usually most evident in the comparison of flying squirrels and nongliding squirrels. This is true of wrist anatomy, probably reflecting the specializations of flying squirrels for the extension of the wing tip and control of it during gliding. In the proximal row of carpals of most squirrels, the pisiform articulates only with the triquetrum, but in flying squirrels there is also a prominent articulation between the pisiform and the scapholunate, providing a more stable base for the styliform cartilage, which supports the wing tip. In the proximal wrist joint, between these carpals and the radius and ulna, differences in curvature of articular surfaces and in the location of ligaments also correlate with differences in degree and kind of movement occurring at this joint, principally reflecting the extreme dorsal flexion and radial deviation of the wrist in flying squirrels when gliding. The distal wrist joint, between the proximal and distal rows of carpals, also shows most variation among flying squirrels, principally in the articulations of the centrale with the other carpal bones, probably causing the distal row of carpal bones to function more like a single unit in some animals. There is little variation in wrist musculature, suggesting only minor evolutionary modification since the tribal radiation of squirrels, probably in the early Oligocene. Variation in the carpal bones, particularly the articulation of the pisiform with the triquetrum and the scapholunate, suggests a different suprageneric grouping of flying squirrels than previously proposed by McKenna (1962) and Mein (1970). J. Morphol. 246:85-102, 2000. Published 2000 Wiley-Liss, Inc.

A mechanical analysis of myomere shape in fish.

An architectural analysis is offered of the trunk muscles in fish, which are arranged in a longitudinal series of geometrically complex myomeres. The myomeres are separated by myosepta, collagenous sheets with complex fibre patterns. The muscle fibres in the myomeres are also arranged in complex three-dimensional patterns. Previously, it has been proposed that the muscle fibre arrangement allows for a uniform strain distribution within the muscle. Physical constraints limit the range of shapes that fibre-reinforced materials such as muscles can adopt, irrespective of their genetic profile. The three-dimensional shapes of myosepta are predicted by mechanical modelling from the requirements for mechanical stability and prescribed muscle fibre arrangements. The model can also be used to study the force transmission and likely locations of ligaments and bones in the myosepta. The model shows that the dorsal and ventral fins are located such that unfavourable mechanical interactions with the trunk muscles are avoided. In bony fish, extensive muscular deformations (notably in the region of the horizontal septum) that would not contribute to bending are avoided by the mechanical support of the skin, intramuscular bones and ribs. In sharks, the skin plays a more prominent role in avoiding such deformations because of the absence of bony elements.