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The arrow indicates the fornix. It arises from the hippocampus and ends in the mamillary body of the hypothalamus. Fornix is an example of association fiber. It is supplied by the anterior cerebral artery.

Nucleus pulposus is derived from the notochord (marked as 1). The other labelled structures are 2 - Ectoderm, 3 - Endoderm, 4 - Intraembryonic mesoderm.

The muscle marked in the above image is the lateral pterygoid muscle and its primary function is depression of the mandible (opening of the mouth). Bilateral contraction of the lateral pterygoid alone causes depression of the mandible (making it the primary function) whereas, protrusion is the result of bilateral contraction of both the medial and lateral pterygoid muscles.

The mandibular nerve passes through the foramen ovale which is marked as A in the above image. Other foramina marked in the above image: B - Foramen spinosum, C - Internal acoustic meatus, D - Jugular foramen.

The structure marked with the asterisk in the electron micrograph indicates presynaptic secretory vesicles. The structure marked with the arrowhead is postsynaptic density.

The secretory vesicles are synthesized by the neurons and are involved in electrochemical signalling in the brain and neuromuscular junctions.

On electron microscopy:

• Mitochondria appear as round or elliptical bodies of 0.5-2.0 micron long on an electron microscope, consisting of an outer and an inner mitochondrial membrane, cristae, and mitochondrial matrix.
• Golgi bodies (or Golgi apparatus) appear as stacks of flatenned membranous cisternae surrounded by clusters of vesicles.
• Ribosomes may be attached to the membrane of the rough endoplasmic reticulum (as shown in the image below), or else, they may exist as monosomes or as a chain of granular structures called polyribosomes associated with mRNA.

In the given image the structure marked B represents the lateral pterygoid muscle which is responsible for the opening of the mouth.

Lateral pterygoid:

• Origin -
• Upper head - Infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone.
• Lower head - Lateral surface of the lateral pterygoid plate.
• Insertion - It is inserted into the pterygoid fovea, capsule of the temporomandibular joint, and the articular disc.
• Nerve supply - Lateral pterygoid nerve which is a branch of the trigeminal nerve.
• Other structures marked:

A - Temporalis

C - Masseter

D - Medial pterygoid

The marked foramen is the superior orbital fissure and the abducens nerve passes through it.

The abducens nerve is the 6th cranial nerve and arises from the brainstem at the pontomedullary junction. It runs through the Dorello's canal which is present at the medial most end of the petrous ridge and then enters the cavernous sinus where it lies lateral to the internal carotid artery. It enters the orbit through the superior orbital fissure within the common tendinous ring and supplies the lateral rectus.

Other options:

Spinal accessory nerve passes through the foramen magnum along with the medulla oblongata and the verterbral arteries

Ophthalmic artery passes through the optic canal along with the optic nerve.

Middle meningeal artery and vein pass through the foramen spinosum along with the meningeal branch of mandibular nerve.

The structure marked A is the splenium of the corpus callosum and it is connected to the striate cortex.

The body of the corpus callosum arches posteriorly and ends as the thickened posterior portion called the splenium. The fibers from the splenium form the forceps major and arch backward into the occipital lobe (striate cortex).

The hippocampus is not connected directly to the splenium, but situated inferior to the splenium. The image given below shows the parts of the corpus callosum.