Answer Key — RGUHS QP Code 5501 (Anatomy MCQs, Q18-27)

• (i) Plane describing midline structures in the brain: A. Sagittal (specifically the midsagittal plane shows midline structures like corpus callosum, septum pellucidum, brainstem).
• (ii) Plane dividing body into anterior and posterior halves: D. Coronal (frontal plane).

• (i) Three primary germ layers: D. Ectoderm, Intraembryonic mesoderm, Endoderm (gastrulation converts the bilaminar disc into a trilaminar disc of these three definitive layers; "extraembryonic" structures like amnion/yolk sac wall are not primary germ layers of the embryo proper).
• (ii) Structure developing from all three germ layers: A. Tympanic membrane — outer cuticular layer (ectoderm), middle fibrous layer (mesoderm), inner mucosal layer (endoderm, from 1st pharyngeal pouch).

• (i) Hybrid muscle involved: D. Brachialis — it's called a "hybrid" muscle because although it lies in the flexor compartment, it receives dual nerve supply. Weak flexion (brachialis is the main pure elbow flexor) with retained partial supination fits injury to brachialis while biceps brachii (the main supinator) is spared.
• (ii) Nerve supply of brachialis: A. Musculocutaneous and radial nerves (a small lateral slip is classically supplied by a branch of the radial nerve, in addition to the main musculocutaneous supply).

• (i) Nerve injured: C. Ulnar nerve (classic "funny bone" injury — nerve is superficial behind the medial epicondyle).
• (ii) Sign of chronic ulnar nerve compression at elbow: D. Clawing of the 4th and 5th digits ("ulnar claw hand," worse in proximal/chronic lesions).

• (i) Carina is a landmark in: D. Bronchoscopy.
• (ii) Tracheal bifurcation level: B. Lower border of T4 (corresponds to sternal angle/T4-T5 disc level).

• (i) Muscle forming Passavant's ridge: A. Palatopharyngeus muscle (its fibers, along with the superior constrictor, form this ridge that helps velopharyngeal closure).
• (ii) Soft palate muscle supplied by the mandibular nerve (V3): B. Tensor veli palatini (all other palatal muscles are supplied by the pharyngeal plexus/vagus via cranial accessory fibers).

• (i) Nerve injured: B. Spinal accessory nerve (CN XI) — runs superficially through the posterior triangle, vulnerable during lymph node/abscess surgery there; injury causes trapezius palsy (shoulder droop, winging of scapula, weak arm abduction above horizontal).
• (ii) Muscle from the listed options supplied by this nerve: A. Sterno-cleido mastoid (CN XI supplies SCM and trapezius; of the four choices given, only SCM is innervated by the accessory nerve — trapezius itself, the muscle clinically affected here, isn't among the options).

• (i) Nerve carrying taste from anterior 2/3 of tongue: C. Chorda tympani nerve (branch of facial nerve; explains the taste loss alongside facial muscle weakness causing drooling/slurred speech).
• (ii) Middle ear structure it is related to: B. Tympanic membrane (chorda tympani crosses the middle ear cavity medial to the pars flaccida of the tympanic membrane, between the malleus and incus).

• (i) Enlarged central canal is a feature of: D. Syringomyelia.
• (ii) Sensory loss pattern: B. Pain and temperature (dissociated sensory loss — crossing spinothalamic fibers near the central canal are damaged first, while posterior column modalities like position/vibration/touch are preserved until late).

• (i) Cranial nerve affected: D. 6th (Abducens) — classic false localizing sign of raised ICP due to its long intracranial course over the petrous apex.
• (ii) Relation to cavernous sinus: The commonly expected exam answer is B. Lateral wall, but this is worth flagging — strictly, CN VI does not run in a dural wall at all. It travels freely through the body/lumen of the cavernous sinus, inferolateral to the internal carotid artery, which is why it's the cranial nerve most often affected first in cavernous sinus pathology. CN III, IV, V1, and V2, by contrast, run within the lateral wall. If your course/answer key follows BD Chaurasia/Snell teaching strictly, the "correct" concept being tested is that VI is within the sinus proper, not in any wall — worth double-checking against your own course's answer key since the listed options don't include that as a choice.