. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. THE VITREOUS HUMOR 461 certain reptiles in which an eye is developed in connection with the epiphy- sial outgrowths of the diencephalon, the retinal portion of this pineal eye is formed from the inner layer of the bulb, and in this case there is no inversion of the elements. A justification of the exclusion of the optic nerve from the category which includes the other cranial nerves has now been presented. For if the retina be regarded as a portion of the central nervous system, it is clear t
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. THE VITREOUS HUMOR 461 certain reptiles in which an eye is developed in connection with the epiphy- sial outgrowths of the diencephalon, the retinal portion of this pineal eye is formed from the inner layer of the bulb, and in this case there is no inversion of the elements. A justification of the exclusion of the optic nerve from the category which includes the other cranial nerves has now been presented. For if the retina be regarded as a portion of the central nervous system, it is clear that the nerve is not a nerve at all in the strict sense of that word, but is a tract, confined throughout its entire extent within the central nervous system and comparable to such groups of fibers as the direct cerebellar or fillet tracts of that system. The Development of the Vitreous Humor.—It has already been pointed out (p. 448) that a blood-vessel, the hyaloid artery, accom- panied by some mesodermal tissue makes its way into the cavity. Fig. 276.—Reconstruction of a Portion of the Eye of an Embryo of mm. ah, Hyaloid artery; ch, chorioid coat; /, lens; r, retina.—(His.) of the optic cup through the chorioid fissure. On the closure of the fissure the artery becomes enclosed within the optic stalk and appears to penetrate the retina, upon the surface of which its branches ramify. In the embryo the artery does not, however, terminate in these branches as it does in the adult, but is continued on through the cavity of the optic cup (Fig. 276) to reach the lens, around which it sends branches to form the tunica vasculosa lentis. According to some authors, the formation of the vitreous humor is closely associated with the development of this artery, the humor being merely a transudate from it, while others have maintained that it is a derivative of the mesoderm which accompanies the vessel, and is therefore to be regarded as a peculiar gelatinous form of. Please note
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