Topographical anatomy of the dog / by O. Charnock Bradley.

  • Bradley, O. Charnock (Orlando Charnock), 1871-1937.
Date:
1927
Catalogue details

Licence: In copyright

Credit: Topographical anatomy of the dog / by O. Charnock Bradley. Source: Wellcome Collection.

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    from the foramen magnum, where it is continuous with the medulla oblongata of the brain, to the seventh lumbar vertebra. Its caudal extremity rapidly tapers, thus forming the conus medullaris, beyond which is the filuni terniinale. The last named is a thin, thread-like structure, mainly composed of pia mater, but containing some small amount of nervous tissue. A certain degree of dorso-ventral flattening is observable in most of the spinal cord, but this is trifling in the thoracic region and absent in the conus medullaris. The thickness of the cord is not uniform. Those parts are thickest from which spring the nerves forming the limb-plexuses. Thus it comes to pass that there are two enlargements, a cervical swelling (intumescentia cervicalis) and a Imnbar swelling (intumescentia lumbalis). The longest stretch with a uniform diameter is the thoracic part of the cord. Leaving each side of the spinal cord are thirty-four or thirty-five spinal nerves (nervi spinales), classified according to the vertebrae behind which they leave the vertebral canal. The number of nerves agrees with the number of vertebrae in the thoracic, lumbar, and sacral regions; but in the cervical region there are eight nerves, the first leaving the vertebral canal by the intervertebral foramen of the atlas. The number of coccygeal nerves is three or four. Each spinal nerve is formed by the union of two roots, a dorsal and a ventral. Each root in its turn is compounded of a number of rootlets that leave the lateral aspect of the cord. The rootlets of the dorsal root leave the cord along a definite line; but those of the ventral root emerge from a narrow longitudinal area. The two roots pierce the dura mater separately, though close together, and join to form the mixed spinal nerve within the intervertebral foramen, except in the sacral and coccygeal regions, where union takes place within the vertebral canal. Immediately before the union is effected the dorsal root expands into an oval grey swelling, the spinal ganglion (ganglion spinale). Because of the disparity in the length of the spinal cord and the vertebral canal that contains it, and because the cord only reaches as far as the seventh lumbar vertebra, it follows that all the spinal nerves do not leave the cord on a level with their foramina of exit. In other words, it is necessary that most of the nerves must travel, for a longer or shorter distance, within the vertebral canal before gaining egress. Only the first six nerves pass straight and immediately from the spinal cord to the intervertebral foramina. At the seventh cervical nerve an obliquity begins and thereafter gradually increases to such a degree that the terminal part of the cord is surrounded by a cluster of nerve roots known as the cauda equma.