. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 550 used to differentiate the bone and cartilage. In cases whera decal- cification was necessary, celloidin was employed for the embedding mass, and the same combination of stains was used. ac. Descriptions. First Stage of Development, (Figs. 1—14.) Embryos of 5 and 6 mm. total body length, although too young to show an}- recognizable skeletal condensations in the ear region, are interesting because of the form of the first visceral cleft. The median region opens broadly into the pharynx. The lateral area is composed of two p
. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 550 used to differentiate the bone and cartilage. In cases whera decal- cification was necessary, celloidin was employed for the embedding mass, and the same combination of stains was used. ac. Descriptions. First Stage of Development, (Figs. 1—14.) Embryos of 5 and 6 mm. total body length, although too young to show an}- recognizable skeletal condensations in the ear region, are interesting because of the form of the first visceral cleft. The median region opens broadly into the pharynx. The lateral area is composed of two parts; one, the larger dorsal region, is of the expected form, a latero- caudal slit opening to the surface, and the other, in the ventral region, an abrupt latero-anterior outpushing which ends blindly a short distance below the epithe- lium. In later stages when the parts of the skeleton become differentiated the reason for such a form is ap- parent. An embryo of 7 mm. total body length (Figs. 1—3) presents the earliest stage in which the precartilage con- densations of the skeletal elements can be recognized. Although their boundaries are by no means definite, still the}' can be easily identified from their relations to one another and to the visceral clefts, nerves, and blood vessels which are more clearly defined. Taking, as a land-mark, the first visceral pouch which is still open, we find anterior to its ventral outpushing in the mandibular arch, a densely packed mass of cells in which we recognize the proton of the quadrate and mandible. Behind the same pouch, in the second. Section of an embryo of 7 mm. total bodj'^ length showing the general morphological relations of the first stage of development. chorda tympani; f. arteria facialis. ganglion faciale; head somite; first visceral pouch; membranous labyrinth; proton of columella; VII ramus dorsalis nervus Please note that these images are extracted from scan
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