CERVICAL FASCIA 347 



muscles; and posteriorly by the hyo-glossus, and the chondro-glossus. Below it forms a part of 

 the medial wall of the space in which the sublingual gland is lodged. Over the dorsum and tip 

 of the tongue it is covered by the mucosa. This likewise covers laterally, in the region of the 

 base of the tongue, the stylo-glossus, hyo-glossus, and the longitudinalis inferior. The Ungual 

 artery runs between the hyo-glossus and the genio-glossus, and along the boundary between the 

 longitudinalis inferior and the genio-glossus to the tip of the tongue. The lingual vein, which 

 lies lateral to the hyo-glossus muscle, takes a similar although much more irregular course. 

 The glosso-pharyngeal nerve passes down medial to the stylo-glossus muscle to the root of the 

 tongue. The Ungual nerve passes along the lateral margin of the tongue external to the stylo- 

 glossus, hyo-glossus, and inferior longitudinal muscles. The hypoglossal nerve hes lateral to 

 the inferior portion of the hyo-glossus muscle and then sinks into the genio-glossus. 



The hyo-glossus muscle is covered lateralh^ below the free portion of the tongue by the mylo- 

 hyoid, digastric, and stylo-hyoid muscles and by the deep part of the submaxiUary gland. 

 Medially it covers in part the middle constrictor of the pharynx. 



The stylo-glossus muscle above the tongue lies medial to the stylo-hyoid and the internal 

 pterygoid muscles and the parotid gland, and between the internal and external carotid arteries. 

 It lies lateral to the superior constrictor of the pharynx. 



Variations. — The genio-glossus often sends a slip to the epiglottis (levator epiglottidis) . 

 It may send some bundles into the superior constrictor of the pharynx (genio-pharyngeus) or 

 to the stylo-hyoid ligament. Various parts of the muscle may be more or less isolated. Of 

 these, a fasciculus from the mental (genial) spine to the tip of the tongue is the most frequent 

 (longitudinalis linguae inferior medius). The hyo-glossus exhibits considerable variation in 

 structure. Some authors consider the chondro-glossus but a portion of this muscle, while 

 Poirier considers it merely the origin of the longitudinalis inferior. The stylo-glossus may be 

 absent on one side or on both. Its origin varies considerably and may be from the angle of the 

 jaw. The muscle may be doubled. 



5. SUPERFICIAL MUSCULATURE OF THE SHOULDER 

 GIRDLE AND THE EXTERNAL CERVICAL FASCIA 



(Figs. 348, 355) 



The stemo-cleido-mastoid is a strong, band-shaped muscle, bifurcated below, 

 which arises from the medial third of the clavicle and the front of the manubrium 

 and is inserted into the mastoid process of the temporal bone and the neigh- 

 bouring part of the occipital. The large, flat, triangular trapezius arises from the 

 occipital bone and the spines of the cervical and thoracic vertebrae and is in- 

 serted into the lateral third of the clavicle and into the acromion and spine of 

 the scapula. The two muscles lie in a well defined layer of fascia which ensheaths 

 the neck beneath the pJatysma, the external cervical fascia. Both muscles bend 

 the head and neck toward the shoulder, rotate and extend the head, and raise 

 the shoulder. The sterno-cleido-mastoid also elevates the thorax and flexes 

 the neck. 



These two superficially placed muscles represent differentiated portions of a musculature 

 found in elasmobranchs and in the amphibia and all higher vertebrates. In sharks this muscula- 

 ture is associated with the musculature of the branchial arches, and, like them, is innervated 

 by the vagus nerve. In the higher vertebrates it is innervated by the vagus or by the spinal 

 accessory nerve, developed in connection with the vagus. To this innervation by a cranial 

 nerve, innervation by cervical nerves is added in those higher vertebrates in which the muscula- 

 ture is more extensively developed. In the human embryo the muscles migrate from their 

 origin in the upper lateral cervical region to the positions found in the adult. 



FASCItE 



The fasciae of the neck and the relations of the muscles are shown in cross-section in figs. 

 347, and 351. 



The tela subcutanea of the head and neck in the upper dorsal region is thick, fibrous, and 

 closely adherent to the underlying muscle fascia. Ventrally in the cervical region it contains 

 the platysma. 



The external cervical fascia (fig. 350) Ues beneath the subcutaneous tissue and the platysma, 

 completely invests the neck and extends cranialward over the parotid gland to the zygoma and 

 the masseteric fascia. The trapezius hes between two closely adherent laminae of the fascia. 

 From the ventral margin of the trapezius it is continued as a thin but strong membrane across 

 the posterior triangle of the neck, between this muscle and the sterno- cleido-mastoid, and is 

 attached below to the clavicle. It invests the sterno-cleido-mastoid with two adherent laminae 

 and extends from the ventral margin of this muscle across the anterior triangle to the mid-line 

 where it is continued into that of the opposite side. In this triangle the fascia is bound to the 

 hyoid bone, and is thus divided into a submaxillary and an infrahyoid portion. The infrahyoid 

 portion is simple and is attached below to the front of the manubrium. The submaxillary 

 portion is attached to the inferior margin of the mandible. It covers the submaxillary gland, 

 and along the inferior margin gives rise to a strong, membranous 'process which passes inward 

 below the gland and, after extending around the tendon of the digastric muscle, becomes united 



