542 



HUMAN ANATOMY. 



directed upward and laterally and are inserted into the outer surfaces of the lower 

 four ribs. 



Nerve-Supply. — From the anterior divisions of the ninth to the twelfth 

 thoracic nerves. 



Action. — To draw the ribs to which it is attached downward and outward. 

 The muscle contracts during inspiration and assists in this act by counteracting the 

 tendency which the costal part of the diaphragm has to expend a portion of its con- 

 traction in drawing the lower ribs upward and inward. 



Variations. — Variations in the extent of their origin are not uncommon in both the posterior 

 serrati. Stretching between them there is an aponeurosis, termed the vertebral aponeurosis, 

 which represents the degenerated portion of a large mnscle-sheet present in the lower mam- 

 malia, of which the two posterior serrati are the persistent upper and lower portions. 



(r) THE HYPOSKELETAL MUSCLES. 

 The hyposkeletal group of muscles is practically unrepresented in the thoracic 



region. 



THE CERVICAL MUSCLES. 



The Deep Cervical Fascia. — The deep cervical fascia (fascia colli) is a 

 well-marked sheet of connective tissue which lies beneath the platysma and forms a 

 complete investment for the neck region, giving off from its deeper surface numer- 

 ous thin lamellae which 'surround the various structures of the neck region. Pos- 



FiG. 540. 



Sterno-hyoid 

 Thyro-hyoid 

 Omo-hyoid 



Arytenoideus 



Inferior constrictor 

 Carotid sheath 

 Prevertebral layer 



Platysma 



Sterno-niastoid 



Longus colli 



Scalenus aiiticus' 



Scalenus medius 



Scalenus posticus 



Trachelo-mastoid 



Levator anguli scapulae 



Splenius colli 



Multifidus spinfe 

 Semispinalis cervicis 



Trapezius 

 Splenius capitis 



Thyroid cartilage 

 Vocal cord 



-Arytenoid cartilage 

 Pharynx 

 Right carotid artery 



Right internal jugular 

 vein 



Vertebral artery 



\ — V cervical vertebra 



Spinal cord 



y' -^Ligamentum nuchae 



Complexus 



Section across neck at lower border of fifth cervical vertebra. 



teriorly the fascia is attached to the ligamentum nuchae and, traced laterally, it is 

 found to divide into two layers which enclose the trapezius and, uniting again at its 

 outer border, are continued forward over the posterior triangle of the neck to the 

 lateral border of the sterno-cleido-mastoid, where it again divides into two layers to 

 enclose that muscle. The two layers again unite at the medial border of the muscle 

 and are continued over the anterior triangle of the neck to the median line, where 

 the fascia becomes continuous with that of the opposite side. 



This is the superficial layer of the deep cervical fascia. Above it is attached 

 to the superior nuchal line and the mastoid process, whence it is continued along 



