. The American journal of anatomy. —hence the followingdigression. ^ CHANGES IN THE PECTORAL WALL CORRELATED WITH THE LATERDEVELOPMENT OF FILAMENTS AND OPERCULUM During the latter part of the sixth day and the beginning ofthe seventh, four different sets of structures make their appear-ance in the pectoral wall, all of which are represented in figure 1:a pair of pectoral grooves {sulci peciorales); 2) a pair of pectoralridges (cristae pectorales); 3) a pair of mesothelial ridges (cris-iae mesoiheliales) and 4) a median epitrichial ridge {cristaepitrichialis). GILL-FILAMENTS IN SAUROPSIDA 211 T
. The American journal of anatomy. —hence the followingdigression. ^ CHANGES IN THE PECTORAL WALL CORRELATED WITH THE LATERDEVELOPMENT OF FILAMENTS AND OPERCULUM During the latter part of the sixth day and the beginning ofthe seventh, four different sets of structures make their appear-ance in the pectoral wall, all of which are represented in figure 1:a pair of pectoral grooves {sulci peciorales); 2) a pair of pectoralridges (cristae pectorales); 3) a pair of mesothelial ridges (cris-iae mesoiheliales) and 4) a median epitrichial ridge {cristaepitrichialis). GILL-FILAMENTS IN SAUROPSIDA 211 The pectoral grooves first appear about the middle of the sixthday and at once deUmit a roughly triangular area whose basecoincides with the intersection of the neck and breast, and whosedownward directed apex lies just above the umbilicus. At firstthe area enclosed by these grooves is transparent throughout,revealing the outlines of the heart beneath. But almost immedi-ately the basal third becomes vascular and much thicker than. Fig. 1 Sketch of the markings on the pectoral wall of a seven-day chick ( C, Ser. 2076; mm.; 6 days, 7 hours) together with three transverse sec-tions of the pectoral wall of the same embryo, X 42 diam. 507, section at levelof cp.; 550, section at level of ; 651, section at level of , , ,lateral and pectoral margins of opercular fold; , opercular notch; , opercu-lar tubercle; , row of branchial filaments; , opaque area; , pectoralridge; , pectoral groove; , epitrichial ridge; cm., mesothelial ridge; Compare with frontal section of pectoral wall in figure 20. the apical portion which retains for some time its non-vascularand transparent character. In fresh specimens the upper portionexhibits a semi-opacity somewhat similar to that of ground is this part which at the beginning of the seventh day givesrise to a series of superficial evaginations which may appearanywhere in this
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Keywords: ., bookauthorwi, bookcentury1900, bookdecade1910, booksubjectanatomy
