. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. THE OPTIC NERVE 459. stalk toward the brain. Their embryonic history has been traced most thoroughly in rat embryos (Robinson), and what follows is based upon what has been observed in that animal. The optic stalk, being an outgrowth from the brain, is at first a hollow structure, its cavity communicating with that of the third ventricle at one end and with that of the optic bulb at the other. When the chorioid fissure is developed, it extends, as has already been described, for some distance
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. THE OPTIC NERVE 459. stalk toward the brain. Their embryonic history has been traced most thoroughly in rat embryos (Robinson), and what follows is based upon what has been observed in that animal. The optic stalk, being an outgrowth from the brain, is at first a hollow structure, its cavity communicating with that of the third ventricle at one end and with that of the optic bulb at the other. When the chorioid fissure is developed, it extends, as has already been described, for some distance along the posterior surface of the stalk and has lying in it a portion of the hyaloid artery. Later, when the lips of the fissure fuse, the artery becomes enclosed within the stalk to form the ar- teria centralis retina of the adult (Fig. 276). By the formation of the fissure the original cavity of the distal portion of the stalk becomes obliterated, and at the same time the ventral and posterior walls of the stalk are brought into con- tinuity with the retinal layer of the op- tic cup, and so opportunity is given for the passage of the axis-cylinders of the ganglion cells along those walls (Fig. 274). At an early stage a section of the proximal portion of the optic stalk (Fig. 275, A) shows the central cavity surrounded by a num- ber of nuclei representing the mantle layer, and surrounding these a non-nucleated layer, resembling the marginal velum and continuous distally with the similar layer of the retina. When the ganglion cells of the latter begin to send out their axis-cylinder processes, these pass into the retinal marginal velum and converge in this layer toward the bottom of the chorioidal fissure, so reaching the ventral wall of the optic stalk, in the velum of which they may be distinguished in rat embryos of 4 mm., and still more clearly in those of 9 mm. (Fig. 275, A). Later, as the fibers become more numerous, they gradually invade the lateral and finally the dor
Size: 1652px × 1513px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookautho, bookcentury1900, bookdecade1910, booksubjectembryology
