. The elements of embryology. Chickens -- Embryos. »â¢] THE CEANIAL NERVES. 137 Schenk (Wien. Sitz. Bericht. 1868) describes all the cells which invest the hypoblast of the digestive tract, as primarily derived from the proto- vertebra?, with the exception of the peritoneal epithelium, which alone, he con- siders, is the representative of the original mesoblast of the splanchnopleure. According to this view, the muscles of the walls of the alimentary canal, and the 'Irypaxial' muscles, are derived from the original protovertebras, quite as much as those muscles which spring out of the muscle-
. The elements of embryology. Chickens -- Embryos. »â¢] THE CEANIAL NERVES. 137 Schenk (Wien. Sitz. Bericht. 1868) describes all the cells which invest the hypoblast of the digestive tract, as primarily derived from the proto- vertebra?, with the exception of the peritoneal epithelium, which alone, he con- siders, is the representative of the original mesoblast of the splanchnopleure. According to this view, the muscles of the walls of the alimentary canal, and the 'Irypaxial' muscles, are derived from the original protovertebras, quite as much as those muscles which spring out of the muscle-plate. In the absence of any satisfactory means of distinguishing the cells of the intermediate cell-mass from those of the protovertebraa, this view must be considered as at least very doubtful. Of! â â '. In the mesoblast, which lies by the side of the hind brain, and which though not divided into protover- tebrae is the prolongation forwards of the same column of mesoblast out of which in the trunk the protovertebra? are formed, there appear on either side in the course of the third day a series of four small opaque masses, somewhat pearshaped with the stalk directed away from the middle line. These are the rudiments of four cranial nerves, of which two lie in front of and two behind the auditory vesicle. The most anterior of these is the rudiment of the fifth nerve (Figs. 25, V. 45, V). Its narrowed outer portion or Fig. 45. -vm. Head of an Embryo Chick of the Third Day (seventy-five hours) viewed SIDEWAYS AS A TRANSPARENT OBJECT (from Huxley). la. cerebral hemispheres. lb. vesicle of the third ventricle. II. mid-brain. III. hind-brain, g. nasal pit. a. optic vesicle. 6. otic vesicle, d. infundi- bulum. e. pineal body. h. notochord. V. fifth nerve. VII. seventh nerve. VIII. united glossopharyngeal and pneumogastric nerves. 1, 2, 3, 4, 5 the five visceral folds. The stage here represented is a little later than that shewn in Eig. 25, with which it should be
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherlondo, bookyear1874
