262 HEAD AND NECK 



immediately divides into two terminal branches the 

 zygomatico- temporal and the zygomatico-facial. 



Ramus Zygomaticotemporalis. The zygomatico -temporal 

 branch runs forwards and upwards upon the lateral wall of the 

 orbit, under cover of the periosteum, and, after receiving a 

 communicating twig from the lacrimal nerve, it enters the 

 zygomatico-orbital canal of the zygomatic bone. That canal 

 conducts it to the anterior part of the temporal region, where 

 it has been examined already (pp. 19 and 170). 



Ramus Zygomaticofacialis. The zygomatico-facial branch 

 also enters a zygomatico-orbital canal, and is finally con- 

 ducted to the face by the zygomatico - facial canal which 

 traverses the zygomatic bone (p. 19). 



PREVERTEBRAL REGION. 



The following are the structures to be displayed in the 

 prevertebral area : 



Vertebral vein. 



Vertebral and cranio-vertebral 

 articulations. 



Prevertebral muscles. 

 Intertransverse muscles. 

 Cervical nerves. 

 Vertebral artery. 



Dissection. To separate the anterior part of the head, with 

 the pharynx, from the posterior part and the vertebral column 

 a somewhat complicated dissection is necessary. Place the 

 head upside down, so that the cut margin of the skull rests upon 

 the table ; divide the common carotid artery, the internal 

 jugular vein, the vagus nerve, and the sympathetic trunk, on 

 each side, at the level of the neck of the first rib ; pull the 

 trachea and oesophagus, together with the great blood-vessels 

 and nerves, away from the anterior surface of the vertebral 

 column. The separation must be effected right up to the base 

 of the skull. At that point great caution must be observed ; 

 otherwise, the pharyngeal wall or the insertions of the pre- 

 vertebral muscles will be damaged. The base of the skull 

 having been reached, the point of the knife should be carried 

 across the basilar portion of the occipital bone, between the 

 pharynx and the prevertebral muscles, to divide the thick in- 

 vesting periosteum. 



The basilar portion of the occipital bone must now be divided 

 by means of a chisel. Still retaining the part upside down, 

 place the skull so that its floor rests upon the end of a wooden 

 block. Then apply the edge of the chisel to the under surface 

 of the basilar portion of the occipital bone, adjust it accurately 

 in the interval between the pharyngeal wall and the prevertebral 

 muscles, and with a wooden mallet drive it through the base of 

 the skull, inclining it, at the same time, slightly backwards. 



