122 HEAD AND NECK 



decussate with their fellows of the opposite side beneath the chin. 

 The posterior fibres ascend into the face, where they have already 

 been followed to their connection with the risorius and the 

 orbicularis oris (p. 7). Cut through the platysma along the 

 anterior border of the sterno-mastoid and turn it upwards, 

 dividing the twigs of the cervical branch of the facial nerve 

 which supply it. Secure the two terminal branches of the 

 nervus cutaneus colli (O.T. transverse cervical nerve), crossing 

 the middle of the sterno-mastoid ; trace its two branches for- 

 wards, and note the union between the upper branch and the 

 cervical branch of the facial nerve, which was found passing 

 downwards and forwards behind the angle of the mandible in 

 a previous dissection (see p. 15^. In the superficial fascia of 

 the submental region and the anterior part of the submaxillary 

 region secure the tributaries of the anterior jugular vein ; trace 

 them downwards to the trunk of the vein, and follow the trunk 

 to the point where it pierces the deep fascia ; then remove the 

 superficial fascia and expose the deep fascia of the anterior 

 region. Note that the deep fascia extends in a continuous layer 

 from the mandible to the sternum and from the sterno-mastoid 

 of one side to that of the other side. Note, further, that it is 

 attached to the body and the greater cornua of the hyoid bone. 

 The latter attachment separates the infra-hyoid muscles, which 

 lie in the lower part of the neck, from the supra-hyoid muscles, 

 which are situated in the region of the floor of the mouth. 



The dissectors will remember that in the course of the dis- 

 section of the posterior triangle they met with several layers of 

 the deep fascia. A similar division into layers exists in the 

 anterior region, and the opportunity should be taken, whilst the 

 fascia is still uninjured, to demonstrate certain of the layers and 

 the presence of the spaces between them. 



The Suprasternal Space. Make a transverse incision 

 through the deep fascia, immediately above the sternum, and 

 two vertical incisions, one along the anterior border of each 

 sterno-mastoid muscle. Carry the latter incisions upwards for 

 about 38 mm. (one and a half inches), and turn the flap of 

 fascia marked out upwards. The space opened into by the 

 reflection of the first layer of deep fascia of the lower part of the 

 neck is the suprasternal space (Burns). Remove the areolar 

 tissue which fills it, find the lower parts of the anterior jugular 

 veins and the transverse anastomosis between them, and expose 

 the second layer of deep fascia, which forms the posterior 

 boundary of the space and covers and binds together the infra- 

 hyoid muscles of opposite sides. Pass the handle of the scalpel 

 downwards along the posterior wall of the space, and note that 

 it terminates, a short distance below the upper border of the 

 sternum, where the second layer of fascia is attached to the 

 posterior surface of the manubrium, immediately above the 

 origins of the infra-hyoid muscles. If the handle of the knife is 

 passed laterally, along the posterior wall of the space, it will 

 pass deep to the sterno-mastoid into the posterior triangle 

 (see p. 34), and if it is pushed upwards it will be stopped by the 

 union of the first and second layers of the deep fascia, about 

 half-way between the sternum and the thyreoid cartilage. The 

 attachments of the second layer of deep fascia of the lower 

 part of the neck may be summarised as follows. It is attached, 



