DISSECTION OF THE HEAD AND NECK. 153 



humeralis, longus colli, scalenus, and rectus capitis anticus major 

 muscles, and to the diaphragm (see phrenic nerve, page 6); (3) cutaneous 

 branches which pierce the mastoido-humeralis and are distributed as 

 the stellate groups already seen. Besides these, the 6th nerve sends 

 branches to the levator anguli scapulae and rhomboideus muscles, and 

 its phrenic branch sends a twig to the brachial plexus. 



The branches of the 7th and 8th nerves are expended in the brachial 

 plexus after each has detached a communicating filament to the middle 

 cervical ganglion, that from the 7th joining the vertebral nerve, while 

 that from the 8th passes to the ganglion independently. 



Directions. — The dissector of the fore limb will now be in a position 

 to separate the limb from the trunk, which will permit the dissection of 

 the remainder of the neck. The levator anguli scapula;, as left by the 

 dissector of the fore limb, must now be entirely removed in order to 

 expose the posterior part of the splenius. The mastoido-humeralis may 

 also be cut away as far forwards as tlie vertebra dentata. The inser- 

 tions of the splenius, trachelo-mastoideus, and complexus muscles into 

 the head are not to be exposed at present, as that would involve the 

 destruction of the muscles of the ear and other structures not yet 

 dissected. 



The Splenius (Plate 27). This is a flat, fleshy muscle of a 

 triangular form, having its fibres directed downwards and forwards. It 

 takes origin from the 2nd, 3rd, and 4th dorsal spines, and from the 

 funicular portion of the ligamentum nuchee. Its origin from the dorsal 

 spines is aponeurotic, and confounded with that of the anterior serratus 

 and complexus muscles. It is inserted into the mastoid crest, the 

 wing of the atlas, and the transverse processes of the succeeding four 

 cervical vertebrae. The mastoid insertion is flat and aponeurotic, and 

 is united to the mastoid tendon of the trachelo-mastoideus. The 

 insertion into the atlas is tendinous and riband-like, and is common to 

 the trachelo-mastoideus and mastoido-humeralis. The other insertions 

 are fleshy. 



Action. — The right and left muscles acting together elevate the 

 head and neck ; acting singly, they incline the head and neck to the 

 side of the acting muscle. 



Directions. — The origin of the splenius should be carefully detached, 

 and the muscle should be raised and turned downwards so as to expose 

 the subjacent structures. Nerves from the superior primary branches 

 of the cervical nerves, and branches from the superior cervical, dorsal, 

 and vertebral arteries, will be foimd entering its deep face. The 

 trachelo-mastoideus and complexus miiscles, now exposed, should be 

 dissected, the branches of nerves and vessels found in connection with 

 them being as far as possible preserved. 



The Trachelo-Mastoideus. This muscle consists of two parallel 



