Part 4: Arteries and Nerves

On one side of the specimen head, re-identify and expose the common carotid artery (previously identified in Chapters 3 & 4) coursing toward the head. Using blunt dissection, trace the common carotid artery to where it splits into the internal carotid a. and external carotid a. (See DG Figs. 5-41, 5-45, and 5-47)

• Identify the internal carotid a. branching dorsally (in the cat this may be absent/partially absent) (See DG Fig. 5-41, 5-45, and 5-47)

  • • At the base/origin of the internal carotid a., identify the bulbous enlargement that is the carotid sinus.

• Identify the external carotid a., which is the larger branch coursing cranially and continuing rostrally in the head. (See DG Figs. 5-41 and 5-45)

Continue to follow the external carotid artery and identify the following branches on your specimen: occipital a., lingual a., facial a. (See DG Figs. 5-41, 5-45, and 5-47)

• The occipital a. is the first branch from the external carotid artery, and courses dorsally, adjacent to the origin of the internal carotid a.

• The lingual a. branches ventrally from the external carotid artery and passes rostrally toward the tongue.

  • • Look for the hypoglossal nerve (cranial nerve XII) that is closely associated with the lingual a. along its course. We will discuss the hypoglossal nerve again later in this chapter.

• The facial a. branches from the external carotid, rostral to the lingual a., and courses medial to the digastricus m. The facial a. then curves laterally to supply the cheek, lips, and nose.

After the facial a., the external carotid a. gives off the caudal auricular a. and then terminates by dividing into the superficial temporal a. and the maxillary a. However, the dissection of these terminal branches can be quite difficult. In the interest of time, these arteries will be dissected on a demonstration specimen for you to view. Be sure to visit the demo area to identify these arteries. (See DG Figs. 5-45, 5-46, and 5-47)

• On a demonstration specimen that has the zygomatic arch removed, attempt to identify the superficial temporal a.

  • • Dissection Note: Keep in mind this artery is often cut as a result of removing the temporalis m. for this deeper dissection, so there may only be a ‘stump’ of the artery to identify.

• On that same demonstration specimen, identify the maxillary a., which is the larger terminal branch of the external carotid a. after the superficial temporal a. is given off. This artery passes rostromedially, just ventral to the temporomandibular joint and then passes through the alar canal.

The demonstration specimen(s) will have the mandible rotated outward to loosen the temporomandibular joint, which will enable you to see/follow the maxillary artery and nerve, and also identify the mandibular nerve. Proceed as directed on the demonstration specimen(s) for steps 5-9 to identify the arteries and nerves described.

• Dissection Note: In this deeper plane of dissection, note that there are additional muscles of mastication that are visible. These are the pterygoid muscles, which will be discussed in more detail within the Application portion of the course, but you need not identify them.

Identify the mandibular n. (branch of trigeminal nerve (CN V)) and the following ‘triad’ of branches (See DG Fig. 5-48) :

• lingual n.: The lingual nerve is the largest and most rostral of the three nerves seen branching from the mandibular nerve. As its name implies, it courses to the tongue; it is sensory to the rostral two thirds of the tongue.

• inferior alveolar n.: The inferior alveolar nerve is in the middle of the ‘triad’ of nerves and enters the mandibular foramen on the medial side of the mandible. It courses alongside the inferior alveolar a. through the mandibular canal, supplying sensory nerves to the teeth.

  • • Dissection Note: The mental nerves exiting through the mental foramina and supplying the lower lip are branches of this nerve. You will dissect the mental nerve(s) later in this chapter.

• mylohyoid n.: The mylohyoid nerve is the most caudal nerve of the three branches, and is technically a caudal branch of the inferior alveolar nerve. It is motor to the mylohyoideus m. and sensory to the skin between the mandibles.

Follow the continuation of the maxillary artery and identify the inferior alveolar a. branching from it. (See DG Figs. 5-46 and 5-47)

• Dissection Note: This branch arises before the maxillary artery passes through the alar canal.

• The inferior alveolar a. courses alongside the inferior alveolar nerve, passing through the mandibular canal.

The maxillary artery gives off two other arteries (that will not be identified) and then passes through the alar canal. As the maxillary a. emerges from the alar canal, attempt to identify the external ophthalmic a. coursing toward the eye/extrinsic muscles of the eye. (See DG Figs. 5-46, 5-47, and 5-51)

The maxillary artery terminates as the infraorbital a. The infraorbital artery enters the maxillary foramen and passes through the infraorbital canal; it emerges from the infraorbital foramen just ventral to the eye. Identify this artery on the demonstration specimens. (See DG Figs. 5-46 and 5-47)

Coursing alongside the maxillary artery, identify the maxillary n. (branch of trigeminal nerve (CN V)). The continuation of the maxillary n. follows the maxillary artery and it terminates as the infraorbital n., which passes through the infraorbital canal and exits the infraorbital foramen, alongside the infraorbital a. (See DG Figs. 5-55)

Return to your dissection specimen at your table and, using blunt dissection, locate and identify the infraorbital a. and infraorbital n. exiting the infraorbital foramen below the eye.

As previously mentioned, the mental nerve(s) exit the mental foramina of the mandible. On your dissection specimen, move to the rostral end of the mandible and use blunt dissection to find and identify the mental nerve(s) where they emerge.

Re-identify the vagosympathetic nerve trunk (previously identified in Chapters 3 & 4) and trace it into the head. Transect muscles as needed to trace the path of the vagosympathetic trunk to the point where it emerges from the skull so you can identify the cervical sympathetic trunk and the vagus nerve (cranial nerve X). (See DG Fig. 5-54)

• Identify the cervical sympathetic trunk and the cranial cervical ganglion rostrally as they emerge from the skull.

• Identify the vagus nerve (cranial nerve X) just caudal to the cervical sympathetic trunk and cranial cervical ganglion as it emerges from the skull.

Identify the hypoglossal nerve (cranial nerve XII) emerging from the skull just lateral to the vagus nerve and trace it ventrally where it is associated with the lingual artery on its way to innervate muscles associated with the tongue. (See DG Fig. 5-41, 5-48, and 5-54)