The elements of embryology (1874) The elements of embryology elementsofembryo01fost Year: 1874 IX.] THE ETHMO-PRESPHENOID PLATE. 231 posterior clinoid walls. But it is in front of the foremost of these that the most noticeable changes take place. From the mid-line of the coalesced trabecule there rises up a high ridge, the ethmo-presphenoid plate. This plate is at first liighest behind. In front and below it sends out a process, the prenasal cartilage, which forms the cartilaginous basis on which the premaxillary region is moulded. 12. Development continues to be very rapid in these parts; an
The elements of embryology (1874) The elements of embryology elementsofembryo01fost Year: 1874 IX.] THE ETHMO-PRESPHENOID PLATE. 231 posterior clinoid walls. But it is in front of the foremost of these that the most noticeable changes take place. From the mid-line of the coalesced trabecule there rises up a high ridge, the ethmo-presphenoid plate. This plate is at first liighest behind. In front and below it sends out a process, the prenasal cartilage, which forms the cartilaginous basis on which the premaxillary region is moulded. 12. Development continues to be very rapid in these parts; and on the seventh day the anterior end of the ethmo-presphenoid plate (Fig. 70, eth and ps) becomes its highest point and forms the retral spike of the ethmoid (Fig. 70, eth). Fig. 70. tcln mk. hh/ b or cbr Side View of the Cartilaginous Cranium of a Fowl on the Seventh Day of Incubation. (From Parker.) pn prenasal cartilage. ahi alinasal cartilage. ale aliethmoid ; immediately below this is the aliseptal cartilage, eth ethmoid, pp pars plana, ps pre- sphenoid. pa palatine, pg pterygoid, z optic nerve, as alisphenoid. q quadrate, st stapes, fr fenestra rotundum. hso horizontal semicircular canal, psc posterior vertical semicircular canal: both the anterior and the posterior semicircular canals are seen shining through the cartilage. so supraoccipital. eo exoccipital. oc occipital condyle, nc notochord. ink Meckel's cartilage, ch cerato-hyal. bh basi-hyal. cbr and ebr cerato- branchial. bbr basibranchial. The prenasal cartilage (Fig. 70, pn) still points down- wards, and by this time are formed the alinasal cartilages (Fig. 70, aln) developed from the trabecular horns, and the aliseptal cartilages which enclose the inferior turbinate (Fig. 70). The basisphenoid grows outwards on each side to form
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