68 DISSECTION OF THE NECK. 



oris and risorius, as far as the fascia covering the parotid gland, or even 

 to the cheek bone. 



The libres have the same appearance in this as in the lower half of the 

 muscle, but they are rather stronger. Below the chin the inner fibres of 

 opposite muscles cross for a distance of about an inch, but those which 

 art 1 superficial do not belong always to the same side. 



Action. The ordinary action of this muscle is confined to the skin of 

 the neck, which it throws into longitudinal wrinkles ; but it can depress 

 the corner of the mouth by the slip prolonged to the face. Through its 

 attachment to the jaw it will assist in opening the mouth. 



Dissection. Raise the platysma to the base of the jaw, and dissect out 

 the branches of the superficial cervical nerve, and the cervical branches 

 of the facial nerve that are beneath it. Clean also the deep fascia of the 

 neck, and the anterior jugular vein which is placed near the middle line. 



The superficial cervical nerve has been traced from its origin in the 

 cervical plexus to its position on the deep fascia of the neck (p. GO) ; but 

 the nerve may arise from the plexus by two pieces. Beneath the platysma 

 it divides into an ascending and a descending branch : 



The ascending branch perforates the platysma, supplying it, and ends 

 in the integuments over the anterior triangle, about half way down the 

 neck. Whilst this branch is beneath the platysma it joins the facial 

 nerve. 



The descending branch likewise passes through the platysma, and is 

 distributed to the teguments below the preceding, reaching as low as the 

 sternum. 



The infra-maxillary branches of the facial or seventh cranial nerve 

 (rami subcutanei colli) (p. 50) pierce the deep cervical fascia, and pass 

 forwards beneath the platysma, forming arches across the side of the neck 

 (fig. 9), which reach as low as the hyoid bone. Most of the branches end 

 in the platysma, but a few filaments perforate it, and reach the integu- 

 ments. Beneath the muscle there is a communication between the branches 

 of the facial and the offsets of the superficial cervical nerve. 



Dissection. Cut across the external jugular vein about the middle, 

 and throw the ends up and down. Afterwards the superficial nerves of 

 the neck may be divided in a line wkh the angle of the jaw, the anterior 

 ends being removed, and the posterior reflected. The great auricular 

 nerve may be cut through and the ends reflected. 



The part of the deep cervical fascia in front of the sterno-mastoideus is 

 stronger than that behind the muscle, and has the following arrangement. 

 Near the sternum the fascia forms a white firm membrane, which is at- 

 tached to that bone ; but higher in the neck it becomes thinner, and is 

 fixed above the lower jaw and the zygoma, covering also the parotid 

 gland. From the ramus of the jaw a piece is prolonged downwards, be- 

 tween the parotid and submaxillary glands, to join the styloid process ; 

 this piece is named the stglo-maxillary ligament. And from the angle of 

 the jaw a strong piece is continued to the sterno-mastoideus, which fixes 

 forwards the anterior border of that muscle. 



Layers of the membrane are prolonged between the muscles ; and that 

 beneath the sterno-mastoid is connected with the sheath of the cervical 

 vessels. One of these beneath the sterno-thyroid muscle, descends in 

 front of the great vessels at the root of the neck to the arch of the aorta, 

 and the pericardium. 



