298 



ESSENTIALS OF ZOOLOGY 



reach the larynx, where it supplies most of the muscles. The 

 peculiarity of distribution is explained by the fact that the 

 heart is developed far forwards and the posterior nerve of the 

 larynx lies behind the vessels named. As the heart is carried 

 posteriorly into its adult position, the nerve retreats with it. 



XI. accessory ; motor, is derived from the dorsal neural 

 crest behind the vagus and in association with the vagus. 

 It arises from the side of the upper part of the spinal cord and 



Thyroid 

 Cricoid 



Recurrent laryngeal 



Trachea 



Right carotid a. 



Right subclavian a. 



Vagus 



Aortic arch. 



Post, vena cava 

 Diaphragm 



Accessory nerve 

 Superior laryngeal 

 Vagus 



Cardiac nerve 



Left carotid 



Phrenic nerve 



ic nerve 



zft subclavian a. 



Recurrent laryngeal 

 Pulmonary nerve 

 Phrenic nerve 

 Spinal nerve 

 Ramus communicans 



Splanchnic nerve 

 " A Coeliac ganglion 



FIG. 139. A diagram of the nerves of the neck and thorax. 



from the side wall of the medulla, and leaves the skull with 

 IX and X. It is supplied to the sternomastoid muscle and 

 the trapezius muscle. 



XII. hypoglossal ; motor, from floor of medulla, leaves the 

 skull by the condylar foramen and supplies the muscles of the 

 tongue, and by a descending branch the sternothyroid and 

 sternohyoid muscles. 



The spinal cord extends from the medulla along the tunnel 

 formed by the neural arches of the vertebrae to the lumbar 

 region, where it ends in a thin prolongation formed by the 

 meninges and called the filum terminale. It is almost com- 

 pletely divided into lateral halves by the deep dorsal and 



