Answers-1, BIO 3220, Skull-Neurocranium


1. Explain cephalization.
Many different animal lineages have undergone cephalization, basically “the evolution of a head.” Cephalization involves concentrating neurons into a brain at one end of the animal and evolving sensory organs at that same end.

2. Describe the neurocranium. What is its function?
The neurocranium is the portion of the skull surrounding the brain, including the elements that surround the olfactory, optic, orbital or sphenotic, and otic or auditory capsules and the anterior end of the notochord (endocranium) and the series of overlying dermal bones (dermocranium). Also called braincase. Its function is for protection.

3. Describe the chondrocranium. Describe the two cartilages that contribute to it and the formation of the ethmoid and basal plates.
The chondrocranium is the part of the neurocranium formed by endochondral ossification and comprising the bones of the base of the skull. Prechordal, or cartilage “in front of” the notochord, and parachordal, or cartilage “beside and behind” the notochord, contribute to the chondrocranium. Parachordal cartilages expand and along with the notochord form the basal plate. Prechordal cartilages expand and join to form an ethmoid plate.

4. Name the sense capsules that contribute to the braincase.
Olfactory capsules, otic capsules, optic capsules

5. Define occipital condyle and foramen magnum.
Occipital condyle – an articular surface on the occipital bone on each side of the foramen magnum by which the skull articulates with the atlas
Foramen magnum – large orifice in the base of the skull through which the spinal cord passes to the cranial cavity and becomes continuous with the medulla oblongata

6. Name the four ossification centers of the neurocranium. Approximate the location of these centers. (See Skull Handout.)
Occipital, otic, sphenoid, ethmoid (See handout for approximate location.)