OF THE TRIANGLES OF THE NECK. 461 



the external carotid by the Stylo-glossus and Stylo-pharyngeus muscles, and 

 the glosso-pharyngeal nerve. 1 



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, an upper or occipital, and a lower 

 or subclavian triangle. 



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 

 Scapulae, and the Middle and Posterior Scaleni muscles. It is covered by the 

 integument, the Platysma below, the superficial and deep fascice ; 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, the descending branches 

 of the cervical plexus and the transversalis colli artery and vein cross the space. 

 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 

 by raising the limb, on account of the ascent of the clavicle, and increased by 

 drawing the arm downwards, when that bone is depressed. This space is covered 

 by the integument, superficial and deep fascia ; 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. Some- 

 times this vessel rises as high as an. inch and a half above the clavicle, or to 

 any point intermediate between this and the usual level. Occasionally, it 

 passes in front of the Scalenus Anticus, or pierces the fibres of that muscle. 

 The subclavian vein lies behind 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 runs vertically downwards behind the posterior 

 border of the Sterno-'mastoid, to terminate in the subclavian vein; it receives 

 the transverse cervical and suprascapular veins, which occasionally form a plexus 

 in front of the artery, and a small vein which crosses the .clavicle from the ce- 

 phalic. The small nerve to the Subclavius also crosses this 'triangle about its 

 middle. A lymphatic gland is also found in the space. 



INTERNAL CAROTID ARTERY. 

 The Internal Carotid Artery commences at the bifurcation of the common 



1 The same remark will apply to this triangle as was made about the inferior carotid triangle. 

 The structures enumerated, as contained in the back part of the space, lie, strictly speaking, 

 beneath the muscles which form the posterior boundary of the triangle ; but as it is very import- 

 ant to bear in mind their close relation to the parotid gland and its boundaries (on account of 

 the frequency of surgical operations ou this gland) all these parts are spoken of together. 



