Petrous apex and subarcuate fossa maturation.

During the first year of life, the bone of the petrous apex grows rapidly. At birth, only 5 mm of bone separates the cochlea from Dorello's canal as compared to 2 cm in the adult. More than half this growth occurs during the first year of life. The subarcuate fossa is a cavity within the superior semicircular canal which reaches from the posterior fossa to the future mastoid in fetuses and nearly to the mastoid antrum in newborns. During the second year of left it is nearly obliterated to form a shallow depression or slit on the posterior aspect of the temporal bone and the variable petromastoid canal which contains the subarcuate artery and vein. Clinical petrositis of infants less that 1 year of age is rare, and provides a challenge for surgery. A case is reported and discussed.

Biological effects of ingested amosite asbestos, taconite tailings, diatomaceous earth and Lake Superior water in rats.

Because amphibole fibers were found in Lake Superior and in Duluth municipal water, this study was initiated to evaluate the carcinogenicity of ingested asbestos. Groups of 22-30 Sprague-Dawley rats were fed asbestos and related materials during their lifetime and were examined at autopsy after spontaneous death. Test materials were unfiltered Duluth city tap water, municipal water reservoir sediment suspension, taconite plant tailings, amosite asbestos (a "low-dose" group at 20 mg/rat . day an a high-dose group at 300 mg/rat . day) and diatomaceous earth; a control group drank fiber-free well water or filtered city tap water. Autopsy studies revealed no significant increase in the incidence of malignant tumors in any experimental group compared with that in the control group.

Distribution of microtubules and microfilaments in developing vestibular sensory epithelium of mouse otocysts grown in vitro.

Otocysts explanted from 12th-gestation-day mice and maintained in organ culture under went a series of developmental changes which paralleled those that occurred in vivo and which resulted in the formation of a sensory epithelium of the vestibular type. At the time of explantation presumptive vestibular sensory epithelium consisted of cells that were undifferentiated, pseudostratified and rapidly proliferating. The only microtubules present were those of the mitotic apparatus. After 4 days of in vitro development cells comprising the presumptive vestibular sensory epithelium were less pseudostratified and more elongate; their nuclei had assumed a basal orientation and there was a clear maginal velum. Longitudinally oriented cytoplasmic microtubules were present at the apices of some cells; they were often grouped around a centriole which may have served as a nucleation centre for their assembly. After 7 days of in vitro development mitosis had ceased and supporting cells had innervated hair cells were present: both types of cells were always longer than they were broad and were often highly asymmetrical. Hair cells were flask- or columnar-shaped, with a nucleus situated in the basal third of the cell. Most mitochondria in hair cells were located in the apical third of the cell. The same distribution of mitochondria and nuclei was evident in supporting cells. Microtubules occurred throughout the length of the supporting cell and were always parallel to its longitudinal axis. In hair cells microtubules were more frequent than in supporting cells: the majority were parallel to the longitudinal axis of the cell but there were two exceptions. First, at the apex of hair cells some microtubules were oriented transversely and diagnonally: these were probably involved in the development and maintenance of the constricted apex of these cells. Secondly, microtubules appeared to be randomly arranged in the narrow region of the cytoplasm between the ventral surface of the nucleus and the base of the hair cells. Microfilaments were confined to the basal third of hair cells where their orientation paralleled that of microtubules. The possible functions of microtubules and microfilaments in the development of hair cells and supporting cells of the mouse vestibular epithelium are discussed.