Articulations of the skull

ARTICULATIONS OF THE SKULL • Most of the bones of the skull are united by sutures.

A few are united by cartilage (synchondrosis) and one (temporomandibular) joint is a synovial joint.

• The sutures have been named according to the bones involved in their formation. E.g. interparietal suture, interfrontal suture, frontoparietal suture, temporoparietal suture etc.

• The principal synchondroses are between (1) basioccipital and post sphenoid (2) post sphenoid and presphenoid (3) parts of occipital. Most of these joints ossify in life.

• A symphysis occurs between the two halves of the ventral ends of the mandible at the median plane. This symphysis does not ossify even in adult life.

• The only movable articulations are the temporomandibular and hyoidean articulations.

MANDIBULAR or TEMPOROMANDIBULAR ARTICULATION Ox: It is a diarthrosis between the condyles of the ramus of the mandible and the squamous temporal. • Ligaments: (1) Capsular Ligament (2) Lateral ligament (3) An inter-articular cartilage or meniscus • Motion: Gliding and angular movements as depression and elevation in opening and closing the mouth.

Rotation on a vertical axis in transverse movements performed during mastication.

MANDIBULAR or TEMPOROMANDIBULAR ARTICULATION Horse: • There is in addition a posterior ligament of elastic tissue attached above to the post glenoid process and below to the next of the ramus.

• Lateral movements are restricted.

Dog: • The inter-articular disc is very thin.

• The posterior ligament is absent.

• There is no transverse movement.

HYOIDEAN ARTICULATIONS In connection with the hyoid bone, five joints are formed on each side viz, (1) basicornual between the body and keratohyoid (2) intercornual between kerato and epihyoid and between epi and stylohyoid (3) temporo hyoidean between stylohyoid and hyoid process of petrous temporal and (4) thyro hyoidean between the thyroid cartilage of larynx and thyrohyoid.

ARTICULATIONS OF THE VERTEBRAL COLUMN • • •

The bones of the vertebral column are serially articulated by their bodies and by the neural processes.

Most of the joints are articulated by some common or common variety of ligaments and therefore called as common vertebral articulations.

There are few joints in the vertebral column, which are not articulated by common ligaments, are called as special vertebral articulations.

Common vertebral articulations The common vertebral articulations are of two kinds: (a) Intercentral, those formed between the bodies of the vertebrae and (b) Interneural, those formed between articular processes of adjacent vertebrae. Associated with these joints are ligaments, some of which extend the whole length of vertebral column-the common ligaments and some are restricted to a single joint-the special ligaments.

The special vertebral articulations are the occipitoatlantoaxial and the coccygeal articulations.

Inter-vertebral discs Each of these is made up of fibro cartilage and is interposed between the bodies to which it is intimately attached.

These discs are thinnest in the dorsal, thicker in the cervical and lumbar and thickest in the coccygeal region.

Each consists of a peripheral fibrous (annulus fibrosus) and a soft central pulpy substance (nucleus pulposus).

There are joint cavities in the cervical intercentral joints, in those between the last cervical and first thoracic and between last lumber and first sacral joints.

Supraspinous ligament The supraspinous ligament is an elastic ligament extending from the sacrum to the occipital bone consists of a dorso- lumbar and a cervical part.

The dorso-lumbar part starts from the sacral spines where it is blended with the dorsal sacroiliac ligament and is attached all along its course to the summits and the first dorsal is continued by the cervical part.

The cervical part or ligamentum nuchae consists of right and left parts, which are continuous with the dorso-lumbar parts. Each division of the cervical part is made up of dorsal funicular portion and a ventral lamellar portion.

The funicular parts of the two sides run forwards and are inserted to the external occipital protuberance.

The lamellar parts is thick is made up of anterior and posterior divisions. The anterior division is paired (right &left), its fibres proceed from the funicular part and becomes inserted to the neural spine of second, third and fourth cervical vertebrae.

The posterior division is single and its fibres arise from the first dorsal and are inserted to the neural spines of the fifth, sixth and seventh cervical vertebrae. The ligamentum nuchae assists the extensors of the head and neck.

THORACIC ARTICULATIONS The thoracic articulations may be divided into • •

extrinsic (costo-vertebral between the ribs and vertebrae) and intrinsic (costo-chondral between the ribs and costal cartilages, chondro-sternal between the costal cartilages and sternum and sternal between the segment of sternum) articulations.