Chapter 33: Head & Neck Surface Anatomy

The scalp features a dense, fibroadipose superficial fascia, while the neck contains a deep cervical fascia subdivided into superficial investing, middle, and deep layers, defining tissue spaces that serve as potential pathways for infection spread but also facilitate surgical dissection. The skeletal framework includes the 28 bones of the skull, which protect the brain within the cranial cavity, along with the intracranial portions of the cranial nerves, meninges (such as the falx cerebri and tentorium cerebelli), and dural venous sinuses. The cervical region is supported by the seven cervical vertebrae, notably characterized by the foramen transversarium (in all but the seventh) and the atypical atlas (C1) and axis (C2). Inferiorly, the hyoid bone is suspended at approximately the fourth cervical vertebral level, and the larynx is framed by cartilages including the thyroid and cricoid. The muscular systems enable crucial functions, encompassing expressive facial movements, mastication, synchronized eyeball motion, swallowing, and articulation. The vascular supply is primarily delivered by the carotid and subclavian artery systems. The external carotid artery branches extensively to supply superficial structures of the face, neck, and scalp, while the internal carotid artery ascends without branches in the neck to supply the ipsilateral cerebral hemisphere and the eye. Arterial supply to the brainstem and posterior circulation is provided by the vertebral arteries, which pass through the cervical transverse processes before uniting to form the basilar artery within the vertebrobasilar system. Venous return from the skull, brain, and much of the neck drains into the deep internal jugular vein, which joins the subclavian vein to form the brachiocephalic vein. Lymphatic drainage is managed by nodes arranged in superficial and deep horizontal rings (including Waldeyer's ring) and vertical chains alongside the carotid sheath, ultimately returning lymph to the systemic circulation via the thoracic or right lymphatic ducts. Innervation is complex, managed by the twelve pairs of cranial nerves that mediate motor, general sensation, special sensation, and critical reflexes (like the gag and corneal reflexes). Additionally, eight pairs of cervical spinal nerves form the cervical plexus (innervating muscles like the diaphragm) and contribute to the brachial plexus. Autonomically, the head contains four pairs of parasympathetic ganglia (ciliary, submandibular, pterygopalatine, and otic), and the sympathetic trunk features usually three cervical ganglia (superior, middle, and inferior/stellate), which deliver postganglionic fibers to target tissues. Surface anatomy provides essential clinical references, such as the bifurcation of the common carotid artery (highly variable, but often near C3), the palpable thyroid cartilage (laryngeal prominence) and cricoid cartilage (useful for emergency airway access), and the bony markers like the pterion and asterion, all of which are critical for precise diagnosis and minimizing damage during surgical procedures.