BRAIN — 3 main parts:
1. Forebrain (Prosencephalon):
– Telencephalon = cerebrum (2 hemispheres + corpus callosum + basal nuclei).
– Diencephalon = thalamus + hypothalamus + pituitary + epithalamus (pineal).
2. Midbrain (Mesencephalon): corpora quadrigemina, tegmentum, cerebral peduncles.
3. Hindbrain (Rhombencephalon): Pons, Medulla oblongata, Cerebellum.

Cerebrum: 4 lobes (frontal, parietal, temporal, occipital).
Cerebellum: coordinator of movement (vermis + 2 hemispheres + flocculonodular lobe).
Brainstem: midbrain + pons + medulla — gives off 12 cranial nerves.

SPINAL CORD:
• Cylindrical CNS extension from foramen magnum to L6 (ox) / L7 (dog).
• Cervical & Lumbosacral enlargements for limb plexuses.
• Ends as conus medullaris + cauda equina.
• Central canal contains CSF.
• Grey matter (H-shaped) inside; white matter outside.

MENINGES (3 layers):
1. Dura mater — outer, tough.
2. Arachnoid mater — middle, web-like; subarachnoid space holds CSF.
3. Pia mater — inner, vascular; hugs CNS surface.

BRAIN — DETAILED ANATOMY

I. CEREBRUM (Telencephalon):
• Two hemispheres connected by corpus callosum.
• Cerebral cortex — outer grey matter; gyri (folds) and sulci (grooves). Most folded in dolphins, chimps; less in cattle/horse; smooth in rodents.
• 4 LOBES: Frontal (motor + executive), Parietal (somatosensory), Temporal (hearing + memory), Occipital (vision).
• Basal nuclei (basal ganglia) — caudate, putamen, globus pallidus → motor control.
• Limbic system — hippocampus, amygdala, fornix → emotion + memory.
• Lateral ventricles — paired CSF cavities.

II. DIENCEPHALON:
• Thalamus — relay station for all sensory info (except olfaction).
• Hypothalamus — homeostasis (temp, hunger, thirst); controls pituitary.
• Epithalamus — pineal gland (melatonin, circadian rhythm).
• 3rd ventricle in midline.

III. MIDBRAIN (Mesencephalon):
• Corpora quadrigemina — 4 mounds: rostral (visual reflexes) + caudal (auditory reflexes) colliculi.
• Cerebral aqueduct connects 3rd → 4th ventricle.
• Cerebral peduncles + tegmentum.

IV. CEREBELLUM:
• Vermis (midline) + 2 hemispheres + flocculonodular lobe.
• Coordinates movement, balance, posture.
• Receives input from inner ear (vestibular), proprioceptors, motor cortex.
• Cortex has 3 layers: molecular, Purkinje, granular.

V. PONS: Bridge of nerve fibres between cerebellum and rest of CNS. Contains pontine nuclei.

VI. MEDULLA OBLONGATA:
• Caudal-most part; continues as spinal cord at foramen magnum.
• Vital centres: respiratory, cardiac, vasomotor.
• Origin of cranial nerves IX, X, XI, XII.

VENTRICULAR SYSTEM (CSF-filled):
2 lateral → 3rd → cerebral aqueduct → 4th → central canal of spinal cord. CSF made by choroid plexus in each ventricle; absorbed by arachnoid villi at dural sinuses.

SPINAL CORD:
• Length: Foramen magnum → L6 in ox (L7 in dog, S1 in horse). Termination = conus medullaris.
• Cauda equina = bundle of lumbar/sacral/coccygeal spinal nerve roots that descend below the conus.
• Cervical enlargement (C6-T2) — supplies forelimb (brachial plexus).
• Lumbosacral enlargement (L4-S2) — supplies hindlimb.
• Internal: H-shaped grey matter (dorsal horns sensory, ventral horns motor, lateral horns autonomic in T1-L3) surrounded by white matter (ascending + descending tracts).

MENINGES:
• Dura Mater — tough outer; in spinal canal forms the dural sac. Epidural space between dura and bone — site of epidural injection.
• Arachnoid Mater — middle, web-like. Subarachnoid space between arachnoid and pia — contains CSF; site of CSF tap (cisterna magna in ox, lumbosacral space in dog).
• Pia Mater — innermost; thin, vascular, adheres to brain/cord surface.

FORMATION OF SPINAL NERVE:
Each spinal nerve forms from union of:
• Dorsal (sensory) root — bears the dorsal root ganglion (cell bodies of sensory neurons).
• Ventral (motor) root — axons of motor + autonomic neurons from the cord.
The two roots join inside the intervertebral foramen → form a mixed spinal nerve, which then divides immediately into a dorsal ramus (to back muscles + skin of dorsum) and a ventral ramus (to limbs + ventro-lateral wall + viscera).