344 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



and neck, serving to move the ears, lips, eyelids, whiskers, etc. The platysma 

 muscle is a visceral muscle originally belonging to the hyoid arch, hence its 

 innervation by the facial nerve. 



e) The fifth or trigeminus nerve: This nerve has three main branches: the 

 ophthalmic, the maxillary, and the mandibular. The former is best studied with 

 the eye since it passes into the orbit. 



To locate the mandibular branch of the trigeminus proceed as follows, free- 

 ing one half of the mandible. Cut through the attachment of the digastric to 

 the mandible and deflect the digastric backward. Cut through the attachments 

 of all of the muscles along the medial surface of the mandible, keeping the knife 

 against the bone. Next, free the lateral or outer surface of the body of the 

 mandible from muscle attachments, chiefly the masseter. Cut through the 

 symphysis of the mandible (place of junction of the two halves of the mandible 

 at their anterior tips). Carefully bend the half of the mandible thus freed out- 

 ward, so as to expose the side of the muscular mass which forms the floor of the 

 mouth and pharyngeal cavities. The main part of the mandibular branch of 

 the trigeminus, the inferior alveolar nerve, will now be seen passing into a fora- 

 men, the mandibular foramen, situated on the medial surface of the mandible. 

 In the rabbit the mylohyoid nerve, another branch of the mandibular, will be 

 noted to the medial side of the inferior alveolar and proceeding ventrally 

 to muscles of the floor of the mouth cavity. The inferior alveolar nerve runs 

 in the interior of the mandible supplying the teeth and then emerges through 

 the mental foramen on the lateral surface of the mandible at the level of the 

 diastema. There the nerve, now named the mental nerve, may be found and 

 followed into the lower lip. 



Trace the inferior alveolar nerve posteriorly. It converges toward another 

 branch of the mandibular nerve, the lingual nerve, which should then be followed 

 forward. It passes into the tongue, lying close to the hypoglossal. The lingual 

 branch of the trigeminus innervates the mucous membrane of the tongue, but 

 is not a nerve of taste. 



Follow both lingual and inferior alveolar nerves centrally again. In front 

 of the tympanic bulla behind the point where the body of the mandible bends 

 dorsally into the ramus of the mandible will be seen the auriculotemporal branch 

 of the mandibular nerve joining the other two. On tracing it peripherally it is 

 found to pass to the skin of the cranial side of the pinna and in the cat also sends 

 branches along the side of the face in company with the branches of the facial. 



The tympanic bulla may now be exposed. Emerging from the bulla will be 

 found a slender nerve which very soon joins the lingual branch of the man- 

 dibular. This is the chorda tympani (so called because it runs in the tympanic 

 membrane), a branch of the facial nerve. Its fibers pass out with the lingual 

 nerve and supply the taste buds on the anterior part of the tongue; it also inner- 

 vates the sublingual and submaxillary salivary glands. 



