. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. OLFACTORY ORGANS. 193 In air-breathing vertebrates, beginning with the dipnoi, a means is developed for drawing air over the sensory surface, the first traces of which are seen in the elasmobranchs. These frequently have an oro-nasal groove, leading from each naris to the angle of the mouth. In some species this groove is practically converted into a tube by the meeting of the walls below. Beginning with the dipnoi and continuing with the amphibia and amniotes (fig. 194) a similar groove is formed on either sid
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. OLFACTORY ORGANS. 193 In air-breathing vertebrates, beginning with the dipnoi, a means is developed for drawing air over the sensory surface, the first traces of which are seen in the elasmobranchs. These frequently have an oro-nasal groove, leading from each naris to the angle of the mouth. In some species this groove is practically converted into a tube by the meeting of the walls below. Beginning with the dipnoi and continuing with the amphibia and amniotes (fig. 194) a similar groove is formed on either side before the formation of skeletal parts. This closes in, the edges of each groove uniting, so that a tube or duct is formed, lead- ing from the naris into the oral cavity, where an internal naris or choana occurs. Later maxillary and premaxillary bones arise ventral to the narial passage, so that the ducts appear to run through the skull. The position of the choanae varies considerably, being just inside the jaws in the amphibia and lower reptiles, farther back in the higher reptiles and the birds and mammals, the nasal passages being cut off from the roof of the primitive mouth by the ingrowth of the palatal processes of the maxillary bones and higher, by similar extensions of the palatines, and in some cases, of the pterygoids (fig. 195). Incomplete closure of the oronasal groove results in the deformity known as 'hare-lip' externally, while 'cleft palate' is the result of failure of palatines, and sometimes of maxillaries to meet below the nasal n. 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 Kingsley, J. S. (John Sterling), 1854-1929. Philadelphia, P. Blakiston's son & co.
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1912
