Anatomy Laboratory Writeups

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The deep head is smaller and originates from the posterior third of the inferior border and from the whole medial surface of the zygomatic arch. This deep head is inserted into the upper half of the ramus and the lateral surface of the coronoid surface of the mandible following a pathway in which the fibres pass inferiorly and anteriorly from origin to insertion point.

What primary differences are there in the size, placement and orientation of the temporalis and masseter muscles between humans and these non-hominin primates?

The masseter and temporalis are both much larger in non-hominin primates than they are in humans.

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the axis articulates anteriorly with the anterior arch of the atlas and posteriorly with the transverse ligament of the atlast. flat inferior facets of the atlas meet with the axis to form lateral atlanto-axial joints. there is pivot articulateon between the dens of the axis and the ring formed by the anterior arch and the transverse ligament of the atlas and is called the atlanto-axial hoint.

The atlas and axis are the two topmost vertebra. The atlas contains no body as it has fused with the body of the axis. the axis contains strong odontoid processes (dens) that rise perpendicularly from upper surface of the body to provide a pivot around which the atlas turns and carries the cranium.

Movement of the neck is coordinated by two different joints. the first is the atlanto-occipital joint which allows for nodding through the flexion and extension at the joint. the concave superior articular facets of the atlas (C1) form this joint with the occipital condyles.

The second type of joint is responsible for shaking or roating the head left and right which happens at the joint between the atlas and axis - the atlanto-axial joint. this is caused by the flat inferior facets of the atlas meeting with the axis (C2) vertebra to form the lateral joint.

Each thoracic vertebrae joins with adjacent vertebrae primarily at the facet joints (located on each side of the spine, towards the back of the spine) and the discs of the thoracic spine (located centrally at the front of the spine) (figure 1). Movements between each adjacent vertebrae are relatively small, but when summated over the entire vertebral column allow considerable mobility.

In the thoracic spine the facet joints are orientated in the coronal plane, which means the primary movements of the thoracic spine are axial rotation and lateral flexion (i.e. twisting and side bending of the spine)

Forms Joints With

• C7 (lowest cervical vertebrae) – T1 forms joints with C7 via the facet joints and disc.

• Each of the vertebrae of the thoracic spine (T1 – T12) connect with the vertebrae above and below via bony processes on each side of the spine which form the facet joints and via the discs located centrally between each spinal segment.

• The ribs - at the costovertebral and costotransverse joints.

• L1 (first lumbar vertebrae) – T12 also forms joints with the first lumbar vertebrae (L1) via the facet joints and disc.