384 SURGICAL ANATOMY. 



the neck. The floor of this space is formed by the anterior belly of the Digastric, 

 the Mylo-hyoid, and Hyo-glossus muscles, and it is covered by the integument, 

 superficial fascia, Platysrna, and deep fascia; ramifying between which are branches 

 of the facial and. ascending filaments of the superficial cervical nerve. This space 

 contains, in front, the subrnaxillary gland; imbedded in the surface of which is the 

 facial artery and vein, and its glandular branches ; beneath this gland, on the sur- 

 face of the Mylo-hyoid muscle, are the submental artery, and the mylo-hyoid artery 

 and nerve. The back part of this space is separated from the front part by the 

 stylo-maxillary ligament ; it contains the external carotid artery, ascending deeply 

 in the substance of the parotid gland; this vessel here lies in front of, and super- 

 ficial to, the internal carotid, being crossed by the facial nerve, and gives off in 

 its course the posterior auricular, temporal, and internal maxillary branches ; more 

 deeply are the internal carotid, the internal jugular vein, and the pneumogastric 

 nerve, separated from the external carotid by the Stylo-glossus and Stylo-pharyn- 

 geus muscles, and the glosso-pharyngeal nerve. 



POSTERIOR TRIANGULAR SPACE. 



The posterior triangular space is bounded, in front, by the Sterno-mastoid 

 muscle ; behind, by the anterior margin of the Trapezius ; its base corresponds to 

 the upper border of the clavicle, its apex to the occiput. This space is crossed, 

 about an inch above the clavicle, by the posterior belly of the Omo-hyoid, which 

 divides it unequally into two triangles, an upper or occipital, and a lower or 

 subclavian. 



The Occipital, the larger of the two posterior triangles, is bounded, in front, 

 by the Sterno-mastoid ; behind, by the Trapezius ; below, by the Omo-hyoid. Its 

 floor is formed from above downwards by the Splenius, Levator anguli scapulas, and 

 the middle and posterior Scaleni muscles. It is covered by the integument, 

 the Platysma below, the superficial and deep fasciae, and crossed, above, by the 

 ascending branches of the cervical plexus : the spinal accessory nerve is directed 

 obliquely across the space from the Sterno-mastoid, which it pierces, to the under 

 surface of the Trapezius; below, it is crossed by the descending branches of the 

 same plexus, and the transversalis colli artery and vein. A chain of lymphatic 

 glands is also found running along the posterior border of the Sterno-mastoid, 

 from the mastoid process to the root of the neck. 



The Subclavian, the smaller of the two posterior triangles, is bounded, above, 

 by the posterior belly of the Omo-hyoid ; below, by the clavicle ; its base, directed 

 forwards, being formed by the Sterno-mastoid. The size of this space varies 

 according to the extent of attachment of the clavicular portion of the Sterno- 

 mastoid and Trapezius muscles, and also according to the height at which the 

 Omo-hyoid crosses the neck above the clavicle. The height also of this space varies 

 much, according to the position of the arm, being much diminished on raising the 

 limb, on account of the ascent of the clavicle, and increased on drawing the arm 

 downwards, when this bone is consequently depressed. This space is covered 

 by the integument, superficial and deep fascias ; and crossed by the descending 

 branches of the cervical plexus. Just above the level of the clavicle, the third 

 portion of the subclavian artery curves outwards and downwards from the outer 

 margin of the Scalenus anticus, across the first rib, to the axilla. Sometimes, 

 this vessel rises as high as an inch and a-half above the clavicle, or to any point 

 intermediate between this and its usual level. Occasionally, it passes in front of 

 the Scalenus anticus, or pierces the fibres of this muscle. The subclavian vein 

 lies beneath the clavicle, and is usually not seen in this space ; but it occasionally 

 rises as high up as the artery, and has even been seen to pass with that vessel 

 behind the Scalenus anticus. The brachial plexus of nerves lies above the artery, 

 and in close -contact with it. Passing transversely across the clavicular margin 

 of the space, are the suprascapular vessels ; and traversing its upper angle in the 

 same direction, the transverse cervical vessels. The external jugular vein descends 



