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The glossopharyngeal nerve is a mixed ninth cranial nerve: it carries pharyngeal and lingual sensation, posterior tongue taste, carotid sensory input, motor fibres to stylopharyngeus, and a secretomotor route to the parotid gland. Its connections explain why its name alone understates its functions.

Rootlets leave the lateral medulla oblongata, behind the olive and above those of the vagus nerve. They cross the posterior cranial fossa and leave through the jugular foramen. Superior and inferior sensory ganglia lie at or near that passage. The cervical trunk descends in relation to the internal carotid artery and internal jugular vein, then turns forwards around stylopharyngeus. It reaches the pharyngeal wall between the superior and middle constrictors and divides towards the posterior tongue, tonsillar region and pharynx. Its topographical association with the vagus does not make the two nerves functionally identical.

The tympanic branch returns through the inferior tympanic canaliculus into the middle ear. Its tympanic plexus supplies the mucosa of the tympanic cavity, auditory tube and related air spaces and communicates with carotid sympathetic fibres. Preganglionic parasympathetic fibres continue through the lesser petrosal nerve to the otic ganglion. Postganglionic fibres then reach the parotid gland with the auriculotemporal nerve, a branch of the mandibular division of the trigeminal nerve. This is a useful example of fibres originating in one cranial outflow and travelling for their last segment with another nerve.^[ref]

The branch to stylopharyngeus is motor; contraction elevates and expands the pharynx during swallowing. Pharyngeal branches contribute to the pharyngeal plexus, together with the vagus nerve and sympathetic connections. The principal motor supply of the pharyngeal constrictors is vagal: membership of a mixed plexus does not justify assigning every fibre or every pharyngeal muscle to the ninth nerve. Tonsillar branches supply the palatine tonsil and neighbouring mucosa. Lingual branches carry ordinary sensation and taste from the posterior third of the tongue, including the vallate papillae even though these lie just anterior to the terminal groove.

The carotid sinus nerve carries information from pressure-sensitive endings in the carotid sinus and from the carotid body's chemical sensors. The first contributes to regulation of blood pressure; the second responds especially to arterial oxygen deficiency, with responses also influenced by carbon dioxide and acidity. These are afferent functions, distinct from the motor and secretory branches.^[ref]

In the modern central account, branchial motor fibres arise from the nucleus ambiguus, parasympathetic fibres from the inferior salivatory nucleus, visceral and taste afferents project towards the solitary nucleus, and relevant general sensory fibres project to the spinal trigeminal system. These nuclear and reflex distinctions refine the gross anatomical description available in 1864. Pharyngeal touch can initiate swallowing and contributes to the afferent limb of the gag reflex, whose principal motor limb is vagal. Ordinary sensation, taste, pharyngeal movement and secretion therefore need separate observations; the absence of one response does not by itself prove loss of every ninth-nerve function.^[ref]

The brain needs continuous, locally matched perfusion within a nearly rigid skull. Its arterial connections, venous drainage, fluid compartments and vascular regulation meet different parts of that requirement. No single arrangement guarantees an unchanging intracranial blood volume or an uninterrupted supply under every condition.

There are two principal arterial approaches: the paired internal carotid arteries and the vertebral arteries, the latter joining as the basilar artery. At the base of the brain, the cerebral arterial circle connects the anterior and posterior supplies through communicating arteries. Connections between superficial cerebral arterial territories provide additional collateral routes. This permits redistribution if one route becomes inadequate, but individual anatomy varies, and some deep penetrating arteries have limited effective collateral supply. The existence of an anatomical circle therefore does not establish that any one artery can be obstructed harmlessly.^[ref]

The bends of the entering arteries and their branching course accompany a distributed vascular resistance and compliance. They should not be described as mechanically abolishing every pulse: cerebral blood flow remains pulsatile. Numerous small branches spread the supply over the surface before penetrating the tissue, while dense capillary networks bring exchange close to neurons and supporting cells.

Superficial and deep cerebral veins drain into dural venous sinuses. These are channels supported by folds and attachments of dura mater, rather than freely collapsible thin-walled veins. Their connections lead chiefly towards the internal jugular veins, with communicating vertebral, diploic and emissary routes providing additional possibilities. The valveless nature of many of these communications allows pressure-dependent changes of direction; it is not an assurance of one-way flow. Head position, neck pressure and the available alternative routes consequently matter to drainage.

The brain, blood and cerebrospinal fluid share the cranial enclosure. A small increase in one component can initially be accommodated by displacement of venous blood and cerebrospinal fluid, including fluid movement towards the spinal compartment. This reserve is finite. When compensation is exhausted, further volume increase can produce a large rise of intracranial pressure and reduce cerebral perfusion pressure. The skull does not make cerebral anaemia physically impossible, as an overly literal historical constant-volume argument might suggest.

A simplified pressure relation, useful in the modern account, iswhere CPP is cerebral perfusion pressure, MAP is mean arterial pressure and ICP is intracranial pressure. The approximation assumes that the effective downstream pressure is represented adequately by ICP; high venous pressure can complicate it. Cerebral autoregulation adjusts arteriolar tone and hence resistance when perfusion pressure changes. It has limited capacity and depends on physiological state, so a fixed universal pressure interval should not be inferred.^[ref]

Local metabolic regulation and neurovascular coupling also match supply to activity. A rise of arterial carbon dioxide tends to dilate cerebral vessels; vigorous overbreathing can lower arterial carbon dioxide and reduce cerebral blood flow. This is distinct from pressure-driven autoregulation. The blood-brain barrier, based principally on specialized capillary endothelium with tight junctions, helps stabilize the chemical environment while permitting regulated exchanges. It is a selective exchange arrangement, not the structure that supports the dural sinuses or generates the arterial pressure. These modern mechanisms refine the anatomical account without attributing all their molecular details to 1865.

The two pneumogastric nerves are the right and left vagus nerves, the tenth cranial nerves: mixed sensory, branchial motor and parasympathetic pathways from the medulla oblongata to the neck, thorax and abdomen. A useful description separates their apparent origin at the surface of the brain from the origins and terminations of their component fibres.

Rootlets emerge in the groove behind the inferior olive, between the glossopharyngeal nerve above and the accessory rootlets below. Branchial motor fibres arise chiefly in the nucleus ambiguus; preganglionic parasympathetic fibres arise in the dorsal motor nucleus of the vagus and, particularly for cardiac control, the nucleus ambiguus. Visceral sensory fibres have their cell bodies chiefly in the inferior vagal ganglion and terminate centrally in the nucleus of the solitary tract; somatic sensory fibres associated with the superior vagal ganglion project to the spinal trigeminal nucleus. Consequently a sensory fibre is not accurately described as originating in a motor nucleus simply because its peripheral nerve emerges nearby.^[ref]

Each vagus nerve leaves the skull through the jugular foramen, with the glossopharyngeal nerve and accessory nerve. It bears the small superior vagal ganglion at the foramen and the larger inferior vagal ganglion below it. Connections include communications with adjacent cranial nerves and the cervical sympathetic nervous system. Traditional descriptions assign fibres joining the vagus nerve from the cranial part of the accessory nerve to the latter peripheral nerve; their modern classification is more nuanced and does not change the peripheral branches being described. In the neck the vagus nerve descends in the carotid sheath, behind and between the internal jugular vein and the internal, then common, carotid artery.

Its meningeal and auricular branches supply small sensory territories of the cranial covering and external ear. Pharyngeal branches contribute to the pharyngeal plexus, supplying much of the soft palate and pharynx; the stylopharyngeus muscle belongs to the glossopharyngeal nerve and the tensor veli palatini muscle to the mandibular division of the trigeminal nerve. The internal branch of the superior laryngeal nerve supplies sensation above the vocal folds; its external branch supplies the cricothyroid muscle. The recurrent laryngeal nerve supplies the other intrinsic laryngeal muscles and sensation below the vocal folds. The right recurrent laryngeal nerve loops beneath the right subclavian artery; the left loops under the aortic arch beside the ligamentum arteriosum. Both return towards the larynx near the groove between trachea and oesophagus.^[ref]

In the thorax, both vagus nerves pass behind the roots of the lungs, contrasting with the anterior course of the phrenic nerves. Cardiac branches join the cardiac plexus; pulmonary branches join the pulmonary plexus. The trunks break up into the oesophageal plexus, then collect principally as an anterior trunk derived from the left vagus nerve and a posterior trunk derived from the right. Through the oesophageal hiatus they reach the stomach; hepatic and coeliac branches distribute to abdominal viscera. Their parasympathetic territory includes foregut and midgut derivatives, extending into the proximal colon, rather than every abdominal and pelvic organ.^[ref] This extensive distribution explains why the level of experimental section is indispensable information.

The main consequences of section can be organized by the interrupted functions:

A discriminating historical experiment would record respiratory movements and heart rate before and after section, distinguish unilateral from bilateral section, and compare an intact airway with an airway bypass. A tracheal cannula can separate obstruction at the glottis from changes in the respiratory rhythm, while the central-versus-peripheral stimulation comparison separates incoming reflex traffic from outgoing motor effects. Later separate-lung recordings confirmed that a change following unilateral section could affect both lungs, supporting a central reflex interpretation rather than simple local paralysis.^[ref] The gastric distinction is also borne out by measurements of persistent acidity after surgical vagotomy, despite major reductions in stimulated gastric acid secretion.^[ref]