448 THE MUSCULAE SYSTEM. 



oesophagus, and pharynx, and the praevertebral muscles. The trachea, oesophagus, 

 and pharynx are likewise encapsuled in cervical fascia, a septal layer passing across 

 the median plane of the neck between the trachea and oesophagus. Lastly, a 

 strong prsevertebral fascia passes across the neck anterior to the praevertebral 

 muscles, and posterior to the oesophagus and pharynx. 



The cervical fascia is attached above to the bones of the skull : superficially to 

 the superior nuchal line of the occipital bone, the mastoid process, the zygoma 

 (over the parotid gland), and the inferior 'border of the mandible ; more deeply to 

 the styloid and vaginal processes of the temporal bone, the great wing of the 

 sphenoid and the basilar part of the occipital bone. This deeper attachment 

 (prcevertebral fascia) is posterior to the parotid gland and pharynx, and is 

 associated with the formation of three ligaments : stylo-mandibular ligament, spheno- 

 mandibular ligament, and pterygo-spinous ligament. The fascia is attached below, 

 through its muscular connexions, to the sternum, first rib, clavicle, and scapula. 

 By means of its connexion with the trachea and the common carotid artery it is 

 carried down behind the first rib into the superior mediastinum, and so becomes 

 continuous with the pericardium. By means of its connexion with the subclavian 

 vessels and brachial nerves it is carried down to the axilla, as the axillary sheath, 

 which becomes connected with the costo-coracoid membrane. 



THE MUSCLES OF THE HEAD. 



The muscles of the head are divisible into three separate groups : the super- 

 ficial muscles, muscles of the orbit, and muscles of mastication. 



Superficial Muscles. 



-^The superficial muscles comprise a large group, including the muscles of the 

 scalp and face, and the platysma in the neck. 



The platysma is a thin quadrilateral sheet extending from chest to face 

 over the side of the neck, between the superficial and deep fasciae. It arises 

 from the deep fascia of the pectoral region. 



It is directed upwards and forwards, and is partly inserted (by its intermediate 

 fibres) into the inferior border of the mandible, becoming connected with the 

 quadrat us labii inferioris and triangularis muscles (Fig. 398, p. 449). The more 

 anterior fibres pass across the median plane of the neck and decussate for a 

 variable distance below the chin with those of the opposite side. The posterior 

 fibres sweep over the angle of the jaw and become continuous with the risorius 

 muscle. The platysma is the rudiment of the cervical portion of the panniculus 

 carnosus of lower animals, in which it has a much more intimate connexion 

 with the muscles of the face than is usually the case in man. 



Nerve-Supply. Cervical branch of the facial nerve. 



Actions. It depresses the mandible and laterally flexes the head. It also throws into folds 

 the skin of the side of the neck. 



The Muscles of the ScaXp. 



The muscles of the scalp comprise the epicranius muscle and the muscles of 

 the auricle. 



M. Epicranius. The epicranius (O.T. occipitofrontalis) is a muscle with four 

 bellies, two posterior and two anterior, and an intervening tendon (the galea 

 aponeurotica) which stretches uninterruptedly across the median plane of the 

 cranium. Each posterior belly (occipitalis) arises as a broad flat band from the 

 lateral two-thirds of the superior nuchal line of the occipital bone. Each anterior 

 belly (frontalis) has no bony attachments; arising from the galea aponeurotica 

 about the level of the coronal suture, it passes downwards to the supra-orbital 

 arch, where it blends with the orbicularis oculi and corrugator supercilii muscles. 

 It extends across the full width of the forehead, and blends in the median plane 

 with the muscle of the opposite side. 



