20 



forwards and outwards, crossing below the jugular vein, to the 

 mastoid process of the skull. 



(c) The sterno-hyoid, nearer the middle line, running from the sternum 



to be attached to the inner third of the cornu majus of the hyoid 

 bone. 



(d) The sterno-thyroid, below, and external to, the sterno-hyoid, run- 



ning from the sternum to the lower border of the thyroid 

 cartilage of the larynx. 



(e) The thyro-hyoid, running from the thyroid cartilage to the hyoid bone. 

 (/) The stylo-hyoid, running from the tip of the cornu majus of the 



hyoid to the styloid process. 

 (g) The mandibular muscles. 

 On the right side, carefully raise up the sterno-mastoid muscle along its 



inner aspect, and fix the muscle in position with a hook, and observe the 



following nerves — 



(a) The pneumogastric (vagus), a stout cord running parallel to the 



carotid artery. Trace this nerve to its point of emergence. Note 

 that it gives off — 



(1) The superior laryngeal, which crosses the carotid artery on its 



dorsal aspect, and goes to the larynx. Very soon after 

 leaving the pneumogastric it gives off superior cardiac 

 (cardiac depressor.) Trace this nerve down the neck, lying 

 alongside the sympathetic, in the connective tissue of the 

 sheath of the common carotid artery. 



(2) The inferior laryngeal (recurrent laryngeal), which passes 



round the subclavian artery. (On the left side it passes round 

 the innominate artery.) 



(3) Branches to the heart, lungs, and oesophagus. 



(b) The hypoglossal, seen running parallel to the cornu majus of the 



hyoid bone, and passing under the stylo-hyoid muscle and over the 

 carotid artery. Trace it forwards to the tongue and backwards to 

 the skull. Note that just before crossing the point of bifurcation 

 of the carotid it gives off the ramus descendens noni, which crosses 

 the carotid on its ventral aspect a little way down. 



(c) The sympathetic, already seen in connection with the superior 



cardiac. Trace it downwards to the inferior cervical ganglion, 

 a little above the junction of the jugular vein with the superior 

 vena cava. 



(cl) The phrenic, already seen between the heart and the lung. (See 

 above, J). 5.) Trace it forwards to its origin from the fourth 

 cervical nerve. [It receives a branch also from the fifth and some- 

 times from the sixth.] 



(") The spinal accessory, a small nerve emerging from the skull with 

 the pneumogastric and the glosso-pharyngeal. (Seen on breaking 

 away the tympanic bulla.) 



