Lateral view of the right side of the ferret head; superior is to the top of the photo.

For comparison, see facial and masticatory muscles of a bat, a cat, a fox, and a tree shrew.

Adapted from Klingener (1979)

We began the dissection by removing the skin around the neck and jaw, a difficult and lengthy procedure. The superficial muscles of facial expression were observed during dissection, but were reflected in order to observe the deeper muscles. All of the muscles of facial expression are innervated by the facial nerve (cranial nerve VII). The first such muscle is the platysma, which is located on the neck superficial to the clavotrapezius. This muscle was extremely thin and broad and was reflected early in the dissection process. The buccinator, which compresses cheeks and maintains food in the oral cavity, was located on the cheek just superior to the mouth. This muscle was of medium size and difficult to see. The orbicularis oculi, the muscle surrounding the eyes that open and close the eyelid, was easily identified because of its circular shape. This muscle was approximately 0.5 centimeters in diameter and completely encircled the eye.

We observed muscles involved in ear movement while skinning the animal. The nocturnal lifestyle of the ferret's wild counterpart, the European polecat, and the importance of hearing in nocturnal animals suggests that it should have well-developed musculature for moving the pinnae. One of these muscles, called the levator aurius longus in the cat, was identified in the ferret. This muscle rotates the ear and was posterior to the pinna. It originated at the base of the pinna and inserted at the nape of the neck.

We found that the ferret has well-developed musculature for moving the vibrissae. Mustelids have a group of guard hairs and sensory hairs located on their muzzle called a mystacial pad [1]. The sensory hairs are innervated by branches of the trigeminal nerve (cranial nerve V) [1]. The thick musculature underlying the muzzle at the mystacial pad serves to move the whiskers.

The major muscles of mastication, the temporalis and the masseter, are innervated by the trigeminal nerve. The temporalis was readily identified because it originates just deep to the skin, on the dorsolateral surface of the skull. It was covered by a thick sheath of fascia that was difficult to remove without damaging the underlying musculature. We used forceps and a probe to separate the fascia from the temporalis. The fascia was then removed with sharp scissors.

The masseter was easily found at the bulge of the cheek. Some of its fibers blend with those of the temporalis muscle near the insertion at the masseteric fossa of the mandible. The masseter was much shorter and thinner than the temporalis.

The comparative sizes of the masseter and temporalis muscles reflect the composition of the animal's diet. Like other carnivores, ferrets have a large temporalis muscle and a relatively reduced masseter. Similar proportions of temporalis and masseter musculature were observed in the cat and fox, two other carnivores. The herbivorous rabbit had a contrasting arrangement of jaw muscles; the temporalis muscle was extremely reduced while the masseter was enormous in comparison.

Carnivores chew their food by slicing it with their carnassial teeth. Having a large temporalis allows the mandible to be pulled upwards and backwards so the carnassial teeth meet before the rest of the teeth. This motion provides the cutting action necessary for mastication of tough meat. Another feature of carnivore jaw anatomy is the relative heights of the mandibular condyle and the occlusal surface of the teeth. They are at the same height, giving the animal more power to slice its food.

Ferrets do not use their hands to kill their prey; they kill small prey such as rats by severing the spinal cord with their teeth [1]. The need for such a powerful crushing mechanism provides an explanation for the ferret's large jaw muscles relative to its size.

References

1. Fox, J.G. 1998. Biology and Diseases of the Ferret (2nd Ed.). Williams & Wilkins, Baltimore.

2. Klingener, D. 1980. Laboratory Anatomy of the Mink (2nd Ed.). William C. Brown, Dubuque, Iowa.

3. Nowak, R.M. 1999. Walker's Mammals of the World (Vol. 1) (6th Ed.). Johns Hopkins University Press, Baltimore.

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