The present work interests in the studying of the optimum stage of neurocranium of Hirundo. The following phenomena have been shown:
1. The formation of the basicranial fenestra has taken place due to a resorption in the pre-existing cartilage of the anterior part of the basal plate.
2. The notochord is exposed dorsally below the hypophyseal and basal fenestra then it is embedded in the basal plate at the occipital region.
3. The commissural exoccipitocapsularis connects the occipital arch and the metotic cartilage.
4. The commissural praevagalis connects the lateral edge of the basal plate with the auditory capsule.
5. The fissure metotica is divided into aperture medialis recessus scalae tympani, foramen jugulare and fissure exoccipitocapsularis.
6. The acoustic foramina are five in number.
7. The cavum metoticum is opened anteriorly but closed posteriorly.
8. The tectum synoticum is formed by fusion of the posterior parts of two auditory capsules only in the mid-line ( otic in origin ).
9. The complete degeneration of the anterior orbital cartilage has been taken place without leaving any traces as planum supraseptale.
10. The fenestra septi interorbitalis is formed by the degeneration of pre-existing cartilage of interorbital septum.
11. The regression process affects the acrochordal cartilage, pila antotica and suprapolar cartilage.
12. The crista parotica, the pila antoticaspuria, the infracarotid commissure and the postorbital cartilage are well developed.
13. The cartilage associated with the palatine is formed.
14. The elements of the nasal capsules originate from three centers of chondrification; the intertrabecula, the planum antorbitale and the paranasal cartilage
|
