VAN 211: Veterinary Histology and Embryology (2+2)

BONES OF THE SKULL

• The earliest indication of the skull is a mass of dense mensenchyme enveloping the cranial end of the notochord and it extends forwards into the nasal region.
• Laterally it becomes continuous with the neuro-cranium, the mesoderm covering and protecting the brain and interiorly with the mesodermal cores of branchial arches.
• Chondrification sets in during the seventh week and it is confined chiefly to the base of the skull-the basioccipital and sphenoidal cartilages.
• The chondrocranium hence refers to the base and neurocranium to the roof and lateral walls.
• Ossification of chondrocranium begins during the third month and forms the occipital, sphenoid ethmoid and pelorus and mastoid parts of the temporal bone.
• The parietals, quamous and tympanic parts of temporal, vomer nasal, lacrimal, malar are all developed in membrane.
• The first branchial arch divides into an upper maxillary and a lower mandibular process.
• The Meckel’s cartilage is the mesenchymal core of the - mandibular process which becomes enveloped by surrounding mesenchyme and finally disappears except at the proximal portion where it is transformed into the sphenomandibular ligaments, malleus and incus. The adult mandible develops in membrane.
• The maxillary process undergoes similar degenerations and the mesoderm surrounding the original cartilage develops into the maxilla and palatine bones.