. The elements of embryology. Chickens -- Embryos. VII.] THE NASAL LABYRINTH. 181 however, it is separated by a shallow depression. This de- pression, which runs nearly horizontally outwards towards the eyeball, is, according to Coste and Kolliker, subsequently con- verted into the lachrymal duct. On the fifth day, the inner nasal processes or lower and outer corners of the fronto-nasal process arching over, unite on each side with the superior maxillary processes. (Com- pare Fig. 57, which, however, is a view of the head of a chick of the sixth day.) In this way each nasal groove is converted
. The elements of embryology. Chickens -- Embryos. VII.] THE NASAL LABYRINTH. 181 however, it is separated by a shallow depression. This de- pression, which runs nearly horizontally outwards towards the eyeball, is, according to Coste and Kolliker, subsequently con- verted into the lachrymal duct. On the fifth day, the inner nasal processes or lower and outer corners of the fronto-nasal process arching over, unite on each side with the superior maxillary processes. (Com- pare Fig. 57, which, however, is a view of the head of a chick of the sixth day.) In this way each nasal groove is converted into a canal, which leads from the nasal pit above, into the cavity of the mouth below, and places the two in direct communication. This canal, whose lining consists of epiblast, is the rudiment of the nasal labyrinth. Fig. Head of a Chick at the Sixth Day from below. (Copied from Huxley's Elements of Comparative Anatomy.) la. cerebral vesicles, a. eye, in which the remains of the choroid slit can still be seen. g. nasal pits. k. fronto-nasal process. I. superior maxillary process. 1. inferior maxillary process or first visceral arch. 2. second visceral arch. x. first visceral cleft between the first and second visceral arches. The cavity of the mouth is seen enclosed by the fronto-nasal process, the superior maxillary processes and the first pair of visceral arches. At the back of it is seen the opening leading into the throat. The nasal grooves leading from the nasal pits to the mouth are already closed over and converted into canals. By the seventh day (Fig. 58), not only is the union of the superior maxillary and fronto-nasal processes completed, and the upper boundary of the mouth thus definitely con-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Foster, M. (Michael), Sir, 1836-1907; Balfour, F
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