expose a portion of the spinal cord and its covering. This usually occurs
near the caudal end of the neural tube. If there is no projection of the spinal
cord or its covering through the bony defect, the condition is generally hid-
den (spina bifida occulta). However, it is termed spina bifida cystica when
spinal material traverses the defect. In a meningocele (answer c),this is a
saclike projection formed only by the meninges. If the projection contains
neural material, it is a meningomyelocele, which is the case for this new-
born. Rachischisis (answer a)is an extreme example of spina bifida cys-
tica in which the neural folds underlying the vertebral defect fail to fuse,
leaving an exposed neural plate. Anencephaly (answer b)occurs when
the cranial neural tube fails to fuse, thus resulting in lack of formation of
forebrain structures and a portion of the enclosing cranium. Hydrocephaly
(answer e)results from blockage of the narrow passageways between the
ventricles or between the ventricles and the subarachnoid space. Resultant
swelling of the ventricles compresses the brain against the cranial vault
and may cause serious mental deficits.
308.The answer is c.(Moore and Dalley, pp 900, 1151–1153.)The sty-
loglossus muscle is innervated by the hypoglossal nerve, which leaves the
posterior cranial fossa by way of the anterior condylar canal. In addition to
the internal jugular vein, the jugular foramen contains the glossopharyngeal
nerve (innervating the stylopharyngeus muscle) (answer d),the vagus
nerve (innervating palatal (answer a),pharyngeal, and laryngeal muscula-
ture), and the spinal accessory nerve [innervating the sternocleidomastoid
(answer b)and trapezius muscles (answer e)].
309.The answer is c.(Moore and Dalley, pp 1083–1084.)The inferior thy-
roid artery arises from the thyrocervical trunk, a branch of the subclavian
artery. The superior thyroid artery arises from the external carotid artery. An
inconsistent thyroid ima artery, when present, may arise from the aortic arch,
the innominate artery, or the common carotid artery. There are no branches
of the internal carotid artery (answer a)and infrequent branches of the com-
mon carotid artery in the neck. The transverse cervical artery (answer d)
supplies the posterior triangle of the neck. The vertebral arteries (answer e)
give off spinal and muscular branches in the neck. The lingual artery only
supplies blood to the tongue (answer b).
Head and Neck Answers 449