548 



HUMAN ANATOMY. 



Digastric, posterior belly 

 Stylo-hyoid (cut) / 



One of these triangles, the posterior, is bounded by the lateral border of 

 the upper part of the trapezius behind and by the lateral border of the sterno- 

 cleido-mastoid in front, and has for its base the upper border of the clavicle 

 between the insertion of these two muscles. The anterior triangle is reversed with 

 respect to the posterior one, having its apex downward and its base above. Its lateral 

 boundary is the medial border of the sterno-cleido-mastoid, its medial boundary is 

 the median line of the neck, and its base is formed by the lower border of the 



mandible and a line 

 Fig. 543. extending horizontally 



backward from the an- 

 gle of the mapdible to 

 the mastoid process. 



Each of these two 

 triangles is again di- 

 visible into subordinate 

 triangles by the mus- 

 cles which cross them. 

 Thus the posterior tri- 

 angle is divided by the 

 inferior belly of the omo- 

 hyoid, which crosses it 

 obliquely, into an upper 

 or occipital triafigle and 

 a lower or subclavian 

 triangle, while the an- 

 terior triangle is divisi- 

 ble into three triangles 

 by the superior belly of 

 the omo-hyoid and the 

 posterior belly of the 

 digastric. The lowest of 

 these triangles, termed 

 the 7nuscnlarox hiferior 

 caj'otid triangle, has its 

 base along the median 

 line and its apex directed laterally, its sides being formed by the sterno-cleido- 

 mastoid below and the superior belly of the omo-hyoid above. The superior carotid 

 triangle has its base along the upper part of the sterno-cleido-mastoid and its apex 

 directed medially ; its sides are formed by the superior belly of the omo-hyoid below 

 and the posterior belly of the digastric above. Finally, the snbiJiaxillary or digastric 

 triangle is the basal portion of the original anterior triangle, and is bounded below 

 by the two bellies of the digastric muscle and above by the line of the lower border 

 of the mandible and its continuation posteriorly to the sterno-mastoid muscle. 



\ Digastric, anterior belly 



SUBMAXILLARY TRIANGLE 

 SUPERIOR CAROTID TRIANGLE 



Omo-hyoid, anterior belly 



INFERIOR CAROTID 



(muscular) TRIANGLE 



SUBCLAVIAN TRIANGLE 



Clavicle 



Omo-hyoid, posterior belly 



Triangles of neck. 



(f) THE HYPOSKELETAL MUSCLES. 



I. Longus colli. 2. Rectus capitis anticus major. 



3. Rectus capitis anticus minor.- 



I. Longus Colli (Fig. 544). 



Attachments.— The longus colli forms an elongated triangular band whose 

 base is towards the median line and the wide-angled apex directed laterally. It may 

 be regarded as consisting of three portions. The medial portioii consists of fibres 

 which arise from the bodies of the upper three thoracic and lower two cervical 

 vertebrae, forming a muscular band which is inserted into the bodies of the three or 

 four upper cervical vertebrae, the slip to the atlas being inserted into its anterior 

 tubercle. From the lower part of the medial portion slips are given off which con- 

 stitute the inferior oblique portion, and are inserted into the transverse processes of 

 the fifth and sixth, and sometimes also of the fourth and seventh, cervical vertebrae. 



