Zygomasseteric system

Last updated

The zygomasseteric system (or zygomasseteric structure) in rodents is the anatomical arrangement of the masseter muscle of the jaw and the zygomatic arch of the skull. The anteroposterior or propalinal (front-to-back) motion of the rodent jaw is enabled by an extension of the zygomatic arch and the division of the masseter into a superficial, lateral and medial muscle. The four main types are described as protrogomorphous, sciuromorphous, hystricomorphous, and myomorphous. [1] :29–32

Contents

Protrogomorphy

Skull of Aplodontia rufa Aplodontia rufa 01 MWNH 267.jpg
Skull of Aplodontia rufa

The members of this grade include nearly all of the pre-Oligocene rodents of North America and Asia and some of those of Europe. Several lineages survive into the Oligocene or early Miocene, with only one species still alive today, the mountain beaver ( Aplodontia rufa ). [2] The molerats (family Bathyergidae) are considered secondarily protrogomorphous since their zygomatic condition is clearly derived from a hystricomorphous ancestor. [3] The rostrum of protrogomorph rodents is unmodified and the infraorbital foramen is small. The superficial masseter originates on the lateral surface of the anterior maxilla and inserts along the ventral margin of the angular process of the mandible. [4] The lateral masseter inserts here as well and originates from the lateral portion of the zygomatic arch. [4] The small medial masseter originates along the medial surface of the zygomatic arch and inserts along the dorsal portion of the mandible at the end of the tooth row. [4]

Sciuromorphy

Skull of an oriental giant squirrel. Note the classic sciuromorphous shape of the anterior zygomatic region. Ratufa skull.JPG
Skull of an oriental giant squirrel. Note the classic sciuromorphous shape of the anterior zygomatic region.

This condition is found in most members of the family Sciuridae (suborder Sciuromorpha), and also in members of the Castoridae, the Eomyidae, and the Geomyoidea. [3] Relative to the primitive protrogomorphous condition, the superficial masseter remains unchanged. [2] The lateral masseter has shifted forward and upward, behind and medial to the superficial masseter. Here it originates from a wide zygomatic plate developed on the anterior (maxillary) root of the zygomatic arch. [4] This shift of origin changed the direction of pull of the anterior part of the lateral masseter from 30 to 60 degrees, greatly strengthening the forward component of the masseter contraction. [2]

Hystricomorphy

Skull of a nutria demonstrating the hystricognathous lower jaw and hystricomorphous zygomasseteric system. Nutriaschadel.jpg
Skull of a nutria demonstrating the hystricognathous lower jaw and hystricomorphous zygomasseteric system.

This condition is found throughout the suborders Hystricomorpha and Anomaluromorpha. In the suborder Myomorpha, it is found in the superfamily Dipodoidea and some fossil Muroidea (such as Pappocricetodon ). Hystricomorphy is also found in the African dormouse Graphiurus , which is a member of the suborder Sciuromorpha. [3]

In hystricomorphs the medial masseter is enlarged and originates on the side of the rostrum (in extreme cases as far forward as the premaxilla), where it then passes through a greatly enlarged infraorbital foramen to insert on the mandible. [4] This gives an almost horizontal resultant to the muscle contraction. [2]

Myomorphy

Gerbil skull displaying the myomorphous condition George's skull1.jpg
Gerbil skull displaying the myomorphous condition

This condition is found in the Muroidea (Myomorpha) and most Gliridae (Sciuromorpha: in the latter it is often referred to as pseudomyomorphy). [3] suggest that the infraorbital foramen of the extinct sciurid subfamily Cedromurinae may have allowed for the passage of the masseter muscle. If true, this subfamily would represent an additional example of myomorphy in the rodent suborder Sciuromorpha.

Myomorphs combine characteristics found in both the sciuromorphous and hystricomorphous rodents. Both the lateral and medial masseter muscles have migrated, and both a large zygomatic plate as well as a large infraorbital foramen are present. [4] This type gives the greatest anteroposterior component of any rodent zygomasseteric system, which might explain the success of the cosmopolitan Muroidea. [2]

Related Research Articles

Articles related to anatomy include:

<span class="mw-page-title-main">Maxilla</span> Upper jaw bone

In vertebrates, the maxilla is the upper fixed bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxillary bones are fused at the intermaxillary suture, forming the anterior nasal spine. This is similar to the mandible, which is also a fusion of two mandibular bones at the mandibular symphysis. The mandible is the movable part of the jaw.

<span class="mw-page-title-main">Zygomatic bone</span> Facial bone

In the human skull, the zygomatic bone, also called cheekbone or malar bone, is a paired irregular bone, situated at the upper and lateral part of the face and forming part of the lateral wall and floor of the orbit, of the temporal fossa and the infratemporal fossa. It presents a malar and a temporal surface; four processes, and four borders.

<span class="mw-page-title-main">Zygomatic arch</span> Cheek bone

In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone, the two being united by an oblique suture ; the tendon of the temporal muscle passes medial to the arch, to gain insertion into the coronoid process of the mandible (jawbone).

<span class="mw-page-title-main">Orbit (anatomy)</span> Cavity or socket of the skull in which the eye and its appendages are situated

In anatomy, the orbit is the cavity or socket/hole of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is about 28 millilitres, of which the eye occupies 6.5 ml. The orbital contents comprise the eye, the orbital and retrobulbar fascia, extraocular muscles, cranial nerves II, III, IV, V, and VI, blood vessels, fat, the lacrimal gland with its sac and duct, the eyelids, medial and lateral palpebral ligaments, cheek ligaments, the suspensory ligament, septum, ciliary ganglion and short ciliary nerves.

<span class="mw-page-title-main">Masseter muscle</span> One of the masticatory muscles in mammals

In anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it is the most superficial and one of the strongest.

<span class="mw-page-title-main">Mountain beaver</span> Species of the genus Aplodontia

The mountain beaver is a North American rodent. It is the only living member of its genus, Aplodontia, and family, Aplodontiidae. It should not be confused with true North American and Eurasian beavers, to which it is not closely related; the mountain beaver is instead more closely related to squirrels, although its less-efficient renal system was thought to indicate greater relative antiquity for the species. There are seven subspecies of mountain beavers, six of which are found in California and three of which are endemic to the state.

<span class="mw-page-title-main">Medial pterygoid muscle</span> Muscle involved in chewing

The medial pterygoid muscle is a thick, quadrilateral muscle of the face. It is supplied by the mandibular branch of the trigeminal nerve (V). It is important in mastication (chewing).

<span class="mw-page-title-main">Sciuromorpha</span> Suborder of mammals

Sciuromorpha ( 'squirrel-like') is a rodent clade that includes several rodent families. It includes all members of the Sciuridae as well as the mountain beaver species.

<span class="mw-page-title-main">Myomorpha</span> Suborder of rodents

The suborder Myomorpha contains 1,524 species of mouse-like rodents, nearly a quarter of all mammal species. Included are mice, rats, gerbils, hamsters, lemmings, and voles. They are grouped according to the structure of their jaws and molar teeth. They are characterized by their myomorphous zygomasseteric system, which means that both their medial and lateral masseter muscles are displaced forward, making them adept at gnawing. As in the hystricognathous rodents, the medial masseter muscle goes through the eye socket, a feature unique among mammals. Myomorphs are found worldwide in almost all land habitats. They are usually nocturnal seed-eaters.

<span class="mw-page-title-main">Blesmol</span> Family of rodents

The blesmols, also known as mole-rats, or African mole-rats, are burrowing rodents of the family Bathyergidae. They represent a distinct evolution of a subterranean life among rodents much like the pocket gophers of North America, the tuco-tucos in South America, and the Spalacidae from Eurasia.

<i>Galesaurus</i> Extinct genus of cynodonts from the Triassic of South Africa

Galesaurus is an extinct genus of carnivorous cynodont therapsid that lived between the Induan and the Olenekian stages of the Early Triassic in what is now South Africa. It was incorrectly classified as a dinosaur by Sir Richard Owen in 1859.

<span class="mw-page-title-main">Infratemporal fossa</span> Cavity that is part of the skull

The infratemporal fossa is an irregularly shaped cavity that is a part of the skull. It is situated below and medial to the zygomatic arch. It is not fully enclosed by bone in all directions. It contains superficial muscles, including the lower part of the temporalis muscle, the lateral pterygoid muscle, and the medial pterygoid muscle. It also contains important blood vessels such as the middle meningeal artery, the pterygoid plexus, and the retromandibular vein, and nerves such as the mandibular nerve (CN V3) and its branches.

<span class="mw-page-title-main">Deep cervical fascia</span>

The deep cervical fascia lies under cover of the platysma, and invests the muscles of the neck; it also forms sheaths for the carotid vessels, and for the structures situated in front of the vertebral column. Its attachment to the hyoid bone prevents the formation of a dewlap.

<span class="mw-page-title-main">Masseteric fascia</span>

The masseteric fascia and parotideomasseteric fascia are fascias of the head varyingly described depending upon the source consulted. They may or may not be described as one and the same structure.

<span class="mw-page-title-main">Buccal space</span>

The buccal space is a fascial space of the head and neck. It is a potential space in the cheek, and is paired on each side. The buccal space is superficial to the buccinator muscle and deep to the platysma muscle and the skin. The buccal space is part of the subcutaneous space, which is continuous from head to toe.

<span class="mw-page-title-main">Coronoid process of the mandible</span> Area of the mandible (jawbone)

In human anatomy, the mandible's coronoid process is a thin, triangular eminence, which is flattened from side to side and varies in shape and size. Its anterior border is convex and is continuous below with the anterior border of the ramus. Its posterior border is concave and forms the anterior boundary of the mandibular notch. The lateral surface is smooth, and affords insertion to the temporalis and masseter muscles. Its medial surface gives insertion to the temporalis, and presents a ridge which begins near the apex of the process and runs downward and forward to the inner side of the last molar tooth.

The montane African climbing mouse or remarkable climbing mouse is a species of rodent in the family Nesomyidae. It is found in Democratic Republic of the Congo, Kenya, Rwanda, Tanzania, and Uganda.

<span class="mw-page-title-main">Zygomatic plate</span> Bony plate in rodent anatomy

In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch (cheekbone). At the back, it connects to the front (maxillary) root of the zygomatic arch, and at the top it is connected to the rest of the skull via the antorbital bridge. It is part of the maxillary bone, or upper jaw, which also contains the upper cheekteeth. Primitively, rodents have a nearly horizontal zygomatic plate. In association with specializations in zygomasseteric system, several distinct morphologies have developed across the order.

<span class="mw-page-title-main">Submasseteric space</span>

The submasseterric space is a fascial space of the head and neck. It is a potential space in the face over the angle of the jaw, and is paired on each side. It is located between the lateral aspect of the mandible and the medial aspect of the masseter muscle and its investing fascia. The term is derived from sub- meaning "under" in Latin and masseteric which refers to the masseter muscle. The submasseteric space is one of the four compartments of the masticator space. Sometimes the submasseteric space is described as a series of spaces, created because the masseter muscle has multiple insertions that cover most of the lateral surface of the ramus of the mandible.

References

  1. Bell, Sean D. (2004). Aplodontid, Scuirid, Castorid, Zapodid and Geomyoid rodents of the Rodent Hill locality, Cypress Hills Formation, Southwest Saskatchewan (Master of Science thesis). Saskatoon: University of Saskatchewan. Retrieved 23 September 2024 via HARVEST.
  2. 1 2 3 4 5 Wood, Albert E. (1965). "Grades and Clades Among Rodents". Evolution. 19: 115–130. doi: 10.1111/j.1558-5646.1965.tb01696.x .
  3. 1 2 3 4 Korth, William W.; Emry, Robert J. (1991). "The skull of Cedromus and a review of the Cedromurinae (Rodentia, Sciuridae)". Journal of Paleontology. 65 (6): 984–994. doi:10.1017/S0022336000033291. S2CID   132211896.
  4. 1 2 3 4 5 6 Hautier, Lionel; Michaux, Jaques; Marivaux, Laurent; Vianey-Liaud, Monique (2008). "Evolution of the zygomasseteric construction in Rodentia, as revealed by a geometric morphometric analysis of the mandible of Graphiurus (Rodentia, Gliridae)". Zoological Journal of the Linnean Society. 154 (4): 807–821. doi: 10.1111/j.1096-3642.2008.00453.x .