Animal muscles generate forces and induce movements at desirable rates. These roles are interactive and must be considered together. Performance of the organism and survival of the species also involve potential optimization of control and of energy consumption. Further, individual variability arising partly via ontogeny and partly from phylogenetic history often has pronounced and sometime conflicting effects on structures and their uses. Hence, animal bodies are generally adequate for their tasks rather than being elegantly matched to them. For muscle, matching to role is reflected at all levels of muscular organization, from the nature of the sarcoplasm and contractile filaments to architectural arrangements of the parts and whole of organs. Vertebrate muscles are often analyzed by mapping their placement and then "explaining" this on the basis of currently observed roles. A recent alternative asks the obverse; given a mass of tissue that may be developed and maintained at a particular cost, what predictions do physical principles permit about its placement. Three architectural patterns that deserve discussion are the classical arrangement of fibers in pinnate patterns, the more recent assumption of sarcomere equivalence, and the issue of compartmentation. All have potential functional implications. 1. The assumption of equivalence of the sarcomeres of motor units allows predictions of the fiber length between sites of origin and insertion. In musculoskeletal systems that induce rotation, the observed (but not the pinnation-associated) insertion angle will differ with the radial lines on which the fibers insert. In a dynamic contraction inducing rotation, a shift of moment arm has no effect for muscles of equal mass. 2. Classical pinnate muscles contain many relatively short fibers positioned in parallel but at an angle to the whole muscle, reducing the per fiber force contribution. However, the total physiological cross-section and total muscle force are thus increased relative to arrangements with fibers parallel to the whole muscle. Equivalent muscles may be placed in various volumetric configurations matching other demands of the organism. The loss of fiber force due to (pinnate, not equivalent) angulation is compensated for by the reduced shortening of fibers in multipinnate arrays. 3. Compartmentation, i.e., the subdivision of muscles into independently controlled, spatially discrete volumes, is likely ubiquitous. Differential activation of the columns of radial arrays may facilitate change of vector and with this of function. Compartmentation is apt to be particularly important in strap muscles with short fiber architecture; their motor units generally occupy columnar, rather than transversely stacked, subdivisions; this may affect recovery from fiber atrophy and degeneration.(ABSTRACT TRUNCATED AT 400 WORDS)

The mechanism of lung ventilation in chelonians has been much debated. Electromyographic studies show that the basic mechanism in the snapping turtle, Chelydra serpentzna, is dependent on the activities of four major respiratory muscles that are capable of varying the volume of the visceral cavity. The precise mechanism utilized varies in response to environmental factors, especially the depth to which the animal is submerged. Chelydra tends to reduce muscular activity to a minimum, and hydrostatic pressure or gravity replaces muscular effort whenever possible. The response is subject to hysteresis. Both the mechanics and pattern of ventilation in CheEydra differ from those of Testudo. The differences appear to be attributable in part to ClzeEydm's markedly reduced plastron and more extensive respiratory musculature and in part to the different habitats occupied by the two species.The mechanism of turtle respiration has attracted the attention of numerous investigators. At least three ventilating mechanisms for breathing while enclosed in a rigid shell have been proposed to act separately or in combination. These are a buccal pump, a limb pump, and a diaphragm-like device involving specialized "respiratory" abdominal muscles in the flanks adjacent to the limbs. Gans and Hughes ('67) have recently confirmed by electromyography that Testudo graeca utilizes respiratory muscles in its respiratory cycle. Respiration is here powered by the action of the M m . transversus abdominis and obliquus abdominis, while the pectoral girdle (moved by contraction of the M m . testocoracoideus and pectoralis among others) serves an accessory role.Testudo graeca is a highly specialized, terrestrial tortoise characterized by an extensive, non-hinged, box-like shell, extreme reduction of the respiratory muscles (the M. diaphragmaticus is absent) and lungs that have a complete attachment to the wall of the pleural cavity. The majority of turtles differ from Testudo in one or more of these characteristics, and it is probable that some of the discrepancies of physiological parameters noted in the literature may be attributed to interspecific differences.The present paper reports parallel experiments with Chelydra serpentina J. MORPH., 128: 195-228.

A•3STRACT.-Eared Grebes (Podiceps nigricollis) use Mono Lake in eastern California as a rest stop during spring migration. Some nonbreeders remain for the summer, and in the autumn the lake becomes a staging area that may accommodate 750,000 returning breeders and young of the year. There the birds become obese by feeding on invertebrates and, if they have not already done so, molt. Most grebes remain several months until a decline in prey populations stimulates further migration. During this period the birds become flightless, and the flight muscles may lose up to 50% of their mass. Myofibers from atrophic birds show evidence of mitochondrial division (or fusion). Even severely atrophic fibers retain a high mitochondrial density (27% vs. 33% in migratory condition), so that relative volume remains stable although absolute volume is reduced. In contrast, intracellular triglyceride droplets are extremely sparse in atrophic fibers, even though most of the birds are carrying >200 g of subcutaneous fat. Mean myofiber diameter increases and decreases with atrophy and hypertrophy. In late autumn, as food availability declines, the birds engage in conspicuous flapping exercises. In the same period, intracellular lipid reappears in the muscles. Within several weeks the muscles are rebuilt to full size and the grebes emigrate. The benefits, if any, of this cycle of muscle atrophy and concomitant obesity, followed by muscle hypertrophy and weight loss, remain obscure.

Neither the possession of large vocabularies or repertoires nor the ability to learn phonations can be precisely correlated with the structural complexity of a syrinx. Hence, some recent investigators have suggested that avian vocal plasticity arises solely from a neurological shift. A simple syrinx, i.e. one with only extrinsic musculature, is subject to certain constraints, however. Its configuration changes as a unit, and the factors responsible for modulating sounds cannot be independently varied. Thus, the temporal characteristics of sound patterns can be varied easily, but rapid juxtaposition of different modulatory patterns is difficult. Intrinsic musculature permits isolation and independent control of syringeal components and thereby simplifies control of modulations. Syringeal complexity may not be an adaptation (i.e. did not evolve under selection) for plastic vocal behavior, but it is permissive of and probably prerequisite for such behavior.

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