332 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



part of the orbit. Follow it forward, noting its distribution to the walls of the 

 nasal cavities. In the floor of the orbit, near its outer margin, locate the maxillary 

 nerve. Trace it forward, noting its branches to the orbit and upper jaw. Trace 

 the maxillary nerve posteriorly, carefully cutting away tissues in its path. 

 Caudad of the orbit it is joined by the mandibular nerve. Trace this, noting 

 branches to muscles and main trunk passing into the lower jaw. Trace the 

 common trunk of the maxillary and mandibular nerve toward the skull and note 

 that they are joined in the skull by the ophthalmic nerve. At the point of union 

 is the semilunar ganglion, lying in the skull. From the ganglion the trigeminus 

 nerve may be traced to its origin from the side of the medulla below the optic 

 lobe. 



g) The facial nerve: This arises from the medulla just back of the root of 

 the trigeminus and passes through the anterior part of the ear capsule, where 

 it will be found by scraping away the latter. 



H) The auditory nerve: This arises close to the facial and passes out with it 

 into the ear capsule to the various parts of which it is distributed. 



i) The glossopharyngeal and the vagus: These nerves arise close together just 

 behind the ear capsule and will be found there by carefully dissecting in the 

 muscles. The glossopharyngeal is the smaller of the two and anterior in position. 

 It enters a ganglion, the petrosal ganglion, beyond which it is distributed to the 

 palate, pharynx, and larynx. The vagus nerve is considerably larger than the 

 glossopharyngeal. It passes laterally parallel and posterior to the glossopharyn- 

 geal and enters its ganglion, the jugular ganglion, which is united with the 

 petrosal ganglion, the two forming a mass. Beyond this the vagus turns pos- 

 teriorly and passes down the neck, supplying respiratory system, heart, and 

 other viscera. Portions of the sympathetic system are intermingled with the 

 ninth and tenth nerves. 



j) The spinal accessory and the hypoglossal: The former passes out with the 

 vagus and is distributed to certain muscles. The hypoglossal is found just 

 posterior to the vagus. It is distributed to certain neck muscles and sends a 

 branch forward to the tongue. 



5. Ventral aspect of the brain. Remove the brain from the cranial cavity, 

 preserving the roots of the cranial nerves as far as possible. Those not kept 

 attached to the brain will be found in the cranial cavity. 



Note form of the olfactory lobes and cerebral hemispheres from the ventral 

 aspect. Between the optic lobes is the diencephalon. In the center of this is 

 the optic chiasma, marked by cross lines. From the optic chiasma the strong 

 white optic tracts pass laterad and dorsad to the optic lobes and dorsal part of 

 the diencephalon. Behind the chiasma is a depressed area, the infundibulum 

 from which the hypophysis extends ventrally. The latter is usually left behind 

 in removing the brain, and will be found in a deep pit, the sella turcica, in the 

 floor of the cranial cavity. The infundibulum bears a central cleft where the 



