Dicondylic skull is characteristic of

a. Amphibia and Mammalia

b. Aves and Mammalia

c. Amphibia and reptilia

d. Reptilia and aves

The human skull is made up of 22 bones. Its main role is to protect the brain and support important structures like the mouth and nose.

Names of the 22 skull bones

• Single bones: Sphenoid, Frontal, Occipital, Ethmoid, Vomer, Mandible, Hyoid
• Paired bones (appear on both sides): Temporal (2), Parietal (2), Lacrimal (2), Nasal (2), Inferior nasal conchae (2), Zygomatic (2), Palatine (2)

Parts of the Skull

The skull has two main regions:

1. Neurocranium (braincase): Protects the brain.
2. Viscerocranium (facial skeleton): Forms the structure of the face.

It can also be divided into the calvarium (skullcap) and facial skeleton.
The hollow space inside is called the cranial cavity, which contains the brain, cranial nerves, blood vessels, meninges, and cerebrospinal fluid (CSF).

Junctions of the Skull

The points where skull bones meet are called sutures (fibrous joints). There are about 33 sutures in the human skull. Some important ones are:

1. Coronal suture
2. Sagittal suture
3. Lambdoid suture
4. Sphenozygomatic suture
5. Sphenofrontal suture
6. Sphenosquamous suture
7. Frontonasal suture
8. Lacrimal-maxillary suture
9. Nasomaxillary suture
10. Frontozygomatic suture

The temporomandibular joint (TMJ) is the only movable (synovial) joint of the skull.

Openings of the Skull

The skull has many openings (foramina and canals) that allow the passage of cranial nerves and blood vessels.

• The largest opening is the foramen magnum at the skull base, where the spinal cord connects to the brain.
• Most foramina are paired (bilateral), but some are single.

Important openings include:

1. Supraorbital foramen (notch)
2. Foramen cecum
3. Cribriform foramina
4. Anterior ethmoidal foramen
5. Posterior ethmoidal foramen
6. Optic canal
7. Superior orbital fissure
8. Foramen rotundum
9. Incisive foramen
10. Greater palatine foramen
11. Sphenopalatine foramen
12. Lesser palatine foramina
13. Inferior orbital fissure
14. Infraorbital foramen
15. Foramen ovale
16. Foramen spinosum
17. Foramen lacerum
18. Internal acoustic meatus
19. Jugular foramen
20. Hypoglossal canal
21. Foramen magnum
22. Stylomastoid foramen