Evidence from cadavers suggestive of entrapment of fifth lumbar spinal nerves by lumbosacral ligaments.

Lumbosacral spines from 51 geriatric-age cadavers (25 men and 26 women) were examined both grossly and under the dissecting microscope for evidence of compression of fifth lumbar spinal nerves by their respective lumbosacral ligaments. These ligaments were found to extend from the transverse process and body of L5 to the ala of the sacrum in 97% of the specimens, and from the transverse process and body of L5 to the promontory of the sacrum in 3% of the specimens. Anterior primary rami of the fifth lumbar spinal nerve were observed to be compressed in 11% (11 of 102) of the specimens examined grossly and under the dissecting microscope. Histologic evidence of chronic compression, as suggested by perineurial and endoneurial fibrosis, peripheral thinning of myelin sheaths, or subjective evidence of a shift in fiber diameter to a population of smaller size fibers was found, deep to the lumbosacral ligament, in three of the 11 nerves judged to be compressed. The information derived is of interest to the clinician whose patient presents with L5 root signs and a myelogram, discogram, and computed tomographic scan which do not show any abnormality. The possibility of extraforaminal compression must be considered as a possible source of the clinical signs.

Morphometry of the lumbar spine: anatomical perspectives related to transpedicular fixation.

The pedicles of lumbar vertebrae were measured both directly and radiographically to determine the differences between the sexes and the accuracy of radiographic measurement. The lumbar pedicles of cadavera of forty-nine patients--twenty-four men and twenty-five women--who died between the ages of sixty and ninety-eight years were measured directly and on radiographs. The pedicles of lumbar vertebrae from fifty-one patients--twenty-three men and twenty-eight women--between the ages of twenty and fifty years who had low-back problems were measured on radiographs and computerized tomographic scans. Comparison revealed that the average transverse and sagittal diameters of the pedicles and the distance from the posterior aspect of the laminar cortex to the anterior aspect of the cortex of the vertebral body along the central axis of the pedicles were 5 to 20 per cent greater in men, but the transverse and sagittal angles of the pedicle did not differ significantly between the sexes. Measurements on radiographs and computerized tomographic scans of the transverse angles of the pedicles and of the distances from the posterior aspect of the laminar cortex to the anterior aspect of the cortex of the vertebral body from the second to the fifth lumbar vertebra were greater than direct measurements, even without magnification. Direct measurements of the diameters of the transverse and sagittal diameters of the pedicle of the fifth lumbar vertebra, however, were greater than the radiographic measurements.

Intradural connections between adjacent cervical spinal roots.

It is not always possible to localize the level of cervical pathology accurately on the basis of clinical signs and symptoms. Intradural intersegmental connections between sensory rootlets occur frequently in the cervical region and have been shown to be clinically and surgically significant. Similar connections between motor rootlets also have been noticed, but their incidence was not reported. Fifty-four human cervical spines were dissected to investigate the incidence of both types of connections. Fifty-three of the 54 specimens had posterior rootlet connections, and nine of the 54 had anterior connections. The preponderant pattern (85%) was for a peripheral dorsal or ventral rootlet to join the central portion of the next rostral or caudal root, and for the two to pass together into the spinal cord. Six distinct patterns were recognized, and a classification system is proposed. These connections may provide a pathway for overlap of sensory dermatomes and motor innervation of the neck and upper extremity. Our observations imply that when a cervical nerve root is injured, small segments of an adjacent root may be equally affected, and the process may be clinically localized one segment higher or lower than it actually is.

Visual accommodation in the flying fox (Pteropus giganteus).

The flying fox, Pteropus giganteus, possesses a papillated retina and was previously thought to lack a mechanism for active accommodation. An investigation of the anatomy and physiology of accommodation in this megachiropteran bat revealed that it has a well developed ciliary muscle and that it can actively accommodate through a range of at least 3.12 D. In addition, it was found that the origin of the retinoscopic reflex does not reside in the receptor layer of the retina, because the focus of the eye is invariant for small changes of angle of refraction.

Craniofacial, occlusal, and masticatory anatomy in bats.

Skull measurements from ten anatomically and behaviorally diverse genera of bats show marked variation in positioning of the face upon the cranium but a relative stability of the site of the mandibular fossa. Factors associated with maintaining occlusion in bats which exhibit dorsally-inclined maxillary toothrows include dorsally angulated mandibular bodies and elevated condyles. Detailed comparisons are made between the generalized morphology of Myotis lucifugus and anatomical extremes represented by Rhinolophus lepidus, Mormoops megalophylla, and Pteropus giganteus. In these four bats, masticatory movements of the teeth and temporomandibular joints, despite marked interspecific variation, appear to relate to a common pattern. The beginning of jaw opening is important for maximal occlusal shear, particularly in Pteropus. Observed differences in the histology of the temporomandibular joints reflect postulated differeces of pressure patterns within them. Differences in skeletal and dental morphology, together with variations in size and orientation of masticatory muscles, could account for known and postulated differences in the four respective chewing patterns, with no major variation from the known muscle firing sequences of Myotis lucifugus. Basic patterns of interaction between central nervous system and masticatory musculature would therefore appear to have undergone minimal modification. This accords with the concept that neural control of mastication is a relatively conservative mechanism; as such, it would appear to have imposed significant limitation upon adaptive change in bats.

Quantitative observations on the nasal epithelia and olfactory innervation in bats. Suggested design mechanisms for the olfactory bulb.

The nasal epithelia of two species of bats were quantified with respect to relative surface areas and olfactory epithelial volumes. In the macrosmatic Aribeus jamaicensis 55.9% of the nasal cavity surface was covered by olfactory epithelium (232.4 mm2), in contrast to only 28.9% in the microsmatic Myotis lucifugus (36.4 mm2). The roles of the various nasal epithelia have been discussed as they may relate to olfaction, respiration and echolocation. In the olfactory bulbs of both species, the estimated concentration of mitral cells approximated at 2,500/mm2 compared to an olfactory nerve concentration of 5/mm2. In Artibeus, calculated total volume of olfactory epithelium was on the order of 16 times greater than in Myotis, and Artibeus' olfactory bulb diameter was twice as great. These findings, together with previously published surface, volume and physiological relationships, suggest a developmental design mechanism for an olfactory bulb in which the number of olfactory receptors increases some 450-fold above an initially established ratio of 2:1 between receptors and mitral cells. Key governing factors could be requisite mechanical rigidity of the cribriform plate of the ethmoid bone and response thresholds of higher brain centers.