DISSECTION OF THE HEAD AND NECK. 167 



The Posterior Auricular Artery (Plate 28) is a collateral branch of 

 the external carotid, detached while that vessel lies over the great 

 cornu of the hyoid bone, and beneath the parotid gland. It divides 

 on the occipito-styloid muscle into an anterior and a posterior branch. 

 The anterior branch ascends in the parotid, and ramifies on the concha 

 behind the posterior edge of its opening, after giving branches to the 

 base of the ear and the interior of the concha. The posterior branch 

 ascends in the parotid gland, and crosses behind the base of the ear, 

 beneath the retrahentes muscles. It then passes under the parieto- 

 auricularis internus, and ascends on the inner surface of the concha as 

 far as its tip. 



The blood is drained away from the ear by the anterior and posterior 

 auricular veins. 



The Anterior Auricular Vein is a larger vessel than the satellite 

 artery. It joins the subzygomatic vein to form the superficial temporal 

 trunk. 



The Posterior Auricular Vein is formed at the base of the ear by 

 two roots which unite at the posterior edge of the parotido-auricularis 

 muscle. It descends at first on the surface of the parotid, and then in 

 its substance, where it joins the jugular vein. 



Nerves : — 



These are derived from the 7th cranial nerve, from the 1st and 2nd 

 cervical nerves, and from the lachrymal nerve of the trifacial. 



The Posterior Auricular Nerve is detached from the 7th cranial 

 nerve as it issues from the stylo-mastoid foramen. It ascends beneath 

 or in the substance of the parotid gland, in company with the artery of 

 the same name ; and, passing immediately behind the mastoid process, 

 it gains the back of the ear, and is distributed to the cervico-auriculares 

 muscles. • ><r 



The Middle Aurici/lar Nerve is detached at the same point as 

 the preceding. It ascends over the annular cartilage, behind the 

 peaked process of the concha, which it enters at its base. It is 

 here distributed to the scattered muscular fibres on the interior of 

 the cartilage. 



The Anterior Auricular Nerve is much larger than either of the 

 preceding nerves. It is given off from the 7th midway between the 

 stylo-mastoid foramen and the edge of the inferior maxilla. It ascends 

 in the parotid, turns over the zygomatic arch, passes downwards 

 beneath the parieto-auricularis muscle, then internal to the root 

 of the supraorbital process of the frontal bone, and terminates below 

 the nasal canthus of the eyelids. It supplies the attolentes muscles 

 as well as the corrugator supercilii and the orbicularis palpebrarum, 

 and its terminal filaments enter the levator labii superioris alseque 

 nasi. 



