326 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



the skull, and finally joins the semilunar ganglion. Follow the maxillary nerve 

 posteriorly. ' Besides the branch below the eyeball already noted there is a 

 branch in the floor of the orbit running obliquely forward. These two branches 

 unite to form the main trunk of the maxillary nerve at the posterior end of the 

 orbit. Trace this nerve posteriorly among the muscles to where it pierces the 

 skull. At this point it is joined by the mandibular branch of the trigeminus. 

 Trace this laterally. After branching into adjacent muscles, the mandibular 

 nerve proceeds ventrally and enters the lower jaw. Mandibular and maxillary 

 branches pass together through a foramen in the skull and connect with the 

 semilunar ganglion. 



/) The facial and auditory nerves: These arise together from the side of the 

 medulla just behind the root of the trigeminus and immediately separate into 

 an anterior facial nerve and a posterior auditory. The latter is distributed to 

 the internal ear. This is situated in the skull opposite the acustico-facial root. 

 This part of the skull may be broken open with the bone forceps. The semi- 

 circular ducts, ampullae, and vestibule of the internal ear will be noted. The 

 auditory nerve will be seen branching among these structures. The facial nerve 

 passes through the anterior part of the ear capsule and will be seen again 

 later. 



g) The glossopharyngeal nerve: This arises by a small root from the medulla 

 immediately posterior to the acustico-facial root and passes out through the 

 posterior part of the ear capsule. 



h) The vagus, the spinal accessory, and the hypoglossal: The vagus and spinal 

 accessory (eleventh) nerves arise together by a number of roots from the side 

 of the medulla posterior to the preceding nerve, the more anterior roots belong- 

 ing to the vagus and the posterior ones to the accessory. On cutting through 

 these roots the more ventrally situated roots of the hypoglossal (twelfth) nerve 

 will be seen. The three nerves pass out from the skull close together. 



*) The abducens nerve: Cut through all of the nerve roots on one side of the 

 brain and tilt the brain toward the opposite side. The abducens nerves will be 

 seen springing from the ventral surface of the medulla at about the same level 

 as the acustico-facial root. 



The seventh, ninth, tenth, and twelfth nerves may be traced farther as 

 follows. Turn the head ventral side up and remove the skin and superficial 

 muscles from the hyoid apparatus. Locate the anterior and posterior horns of 

 the hyoid. On the side of the neck, near the dorsal end of the anterior horn and 

 posterior to it, the hypoglossal nerve will be seen emerging. It branches into 

 the muscles over the anterior horn and sends a branch forward into the tongue 

 muscles. Very near the point of emergence of the hypoglossal but situated more 

 deeply and nearer to the cartilage of the anterior horn will be found the glosso- 

 pharyngeal nerve. It runs between the two horns toward the median ventral 

 line and supplies adjacent muscles and lining of the mouth cavity. Lateral 



