In human anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is 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. The masseter is a thick, somewhat quadrilateral muscle, consisting of two heads and deep; the fibers of the two heads are continuous at their insertion. The superficial head, the larger, arises by a thick, tendinous aponeurosis from the temporal process of zygomatic bone, from the anterior two-thirds of the inferior border of the zygomatic arch, its fibers pass inferior and posterior, to be inserted into the angle of the mandible and inferior half of the lateral surface of the ramus of the mandible. The deep head is much bigger, more muscular in texture, it arises from the posterior third of the lower border and from the whole of the medial surface of the zygomatic arch. Its fibers pass downward and forward, to be inserted into the upper half of the ramus as high as the coronoid process of the mandible.
The deep head of the muscle is concealed, anteriorly, by the superficial portion. Posteriorly, it is covered by the parotid gland. Along with the other three muscles of mastication, the masseter is innervated by the anterior division of the mandibular division of the trigeminal nerve; the innervation pathway is: gyrus precentralis > genu capsula interna > nucleus motorius nervi trigemini > nervus trigeminus > nervus mandibularis > musculus masseter. The action of the muscle during bilateral contraction of the entire muscle is to elevate the mandible, raising the lower jaw. Elevation of the mandible occurs during the closing of the jaws; the masseter parallels the medial pterygoid muscle, but it is stronger and superficial fibres can cause protrusion. To perform an extraoral examination, stand near the patient and visually inspect and bilaterally palpate the muscle. Place the fingers of each hand over the muscle and ask the patient to clench his or her teeth several times; the masseter muscle can become enlarged in patients who habitually clench or grind their teeth and in those who chew gum.
This masseteric hypertrophy is soft. If the hypertrophy is bilateral, asymmetry of the face may still occur due to unequal enlargement of the muscles; this extraoral enlargement may be confused with parotid salivary gland disease, dental infections, maxillofacial neoplasms. However, no other signs are present except those involved in changes in occlusion intraorally such as pain, the enlargement corresponds with the outline of the muscle. Most patients seek medical attention because of comments about facial appearance, this situation may be associated with further pathology of the temporomandibular joint; the muscle undergoes spasm with malignant hyperthermia as do other skeletal muscles, but this one is noted, since it is on the face. Zygomasseteric system
The zygomasseteric system in rodents is the anatomical arrangement of the masseter muscle of the jaw and the zygomatic arch of the skull. The anteroposterior or propalinal motion of the rodent jaw is enabled by an extension of the zygomatic arch and the division of the masseter into a superficial and medial muscle; the four main types are described as protrogomorphous, sciuromorphous and myomorphous. 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; the molerats are considered secondarily protrogomorphous since their zygomatic condition is derived from a hystricomorphous ancestor. 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.
The lateral masseter inserts here as well and originates from the lateral portion of the zygomatic arch. 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; this condition is found in most members of the family Sciuridae, in members of the Castoridae, the Eomyidae, the Geomyoidea. Relative to the primitive protrogomorphous condition, the superficial masseter remains unchanged; the lateral masseter has shifted forward and upward and medial to the superficial masseter. Here it originates from a wide zygomatic plate developed on the anterior root of the zygomatic arch; this shift of origin changed the direction of pull of the anterior part of the lateral masseter from 30 to 60 degrees strengthening the forward component of the masseter contraction. This condition is found throughout the suborders Anomaluromorpha. In the suborder Myomorpha, it is found in some fossil Muroidea. Hystricomorphy is found in the African dormouse Graphiurus, a member of the suborder Sciuromorpha.
In hystricomorphs the medial masseter is enlarged and originates on the side of the rostrum, where it passes through a enlarged infraorbital foramen to insert on the mandible. This gives an horizontal resultant to the muscle contraction; this condition is found in the Muroidea and most Gliridae. 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 histricomorphous rodents. Both the lateral and medial masseter muscles have migrated, both a large zygomatic plate as well as a large infraorbital foramen are present; this type gives the greatest anteroposterior component of any rodent zygomasseteric system, which might explain the success of the cosmopolitan Muroidea
Aelius Galenus or Claudius Galenus Anglicized as Galen and better known as Galen of Pergamon, was a Greek physician and philosopher in the Roman Empire. Arguably the most accomplished of all medical researchers of antiquity, Galen influenced the development of various scientific disciplines, including anatomy, pathology and neurology, as well as philosophy and logic; the son of Aelius Nicon, a wealthy architect with scholarly interests, Galen received a comprehensive education that prepared him for a successful career as a physician and philosopher. Born in Pergamon, Galen travelled extensively, exposing himself to a wide variety of medical theories and discoveries before settling in Rome, where he served prominent members of Roman society and was given the position of personal physician to several emperors. Galen's understanding of anatomy and medicine was principally influenced by the then-current theory of humorism, as advanced by ancient Greek physicians such as Hippocrates, his theories influenced Western medical science for more than 1,300 years.
His anatomical reports, based on dissection of monkeys the Barbary macaque, pigs, remained uncontested until 1543, when printed descriptions and illustrations of human dissections were published in the seminal work De humani corporis fabrica by Andreas Vesalius where Galen's physiological theory was accommodated to these new observations. Galen's theory of the physiology of the circulatory system remained unchallenged. 1242, when Ibn al-Nafis published his book Sharh tashrih al-qanun li’ Ibn Sina, in which he reported his discovery of the pulmonary circulation. Galen saw himself as both a physician and a philosopher, as he wrote in his treatise entitled That the Best Physician Is Also a Philosopher. Galen was interested in the debate between the rationalist and empiricist medical sects, his use of direct observation and vivisection represents a complex middle ground between the extremes of those two viewpoints. Many of his works have been preserved and/or translated from the original Greek, although many were destroyed and some credited to him are believed to be spurious.
Although there is some debate over the date of his death, he was no younger than seventy when he died. In medieval Europe, Galen's writings on anatomy became the mainstay of the medieval physician's university curriculum, but because of the collapse of the Roman Empire in the West they suffered from stasis and intellectual stagnation. However, in the Eastern Roman Empire and the Abbasid Caliphate they continued to be studied and followed; some of Galen's ideas were incorrect. Greek and Roman taboos had meant that dissection was banned in ancient times, but in Middle Ages it changed: medical teachers and students at Bologna began to open human bodies, Mondino de Luzzi produced the ﬁrst known anatomy textbook based on human dissection. Galen's original Greek texts gained renewed prominence during the early modern period. In the 1530s, Belgian anatomist and physician Andreas Vesalius took on a project to translate many of Galen's Greek texts into Latin. Vesalius's most famous work, De humani corporis fabrica, was influenced by Galenic writing and form.
Galen's name Γαληνός, Galēnos comes from the adjective "γαληνός", "calm". Galen describes his early life in On the affections of the mind, he was born in September AD 129. His father, Aelius Nicon, was a wealthy patrician, an architect and builder, with eclectic interests including philosophy, logic, astronomy and literature. Galen describes his father as a "highly amiable, just and benevolent man". At that time Pergamon was a major cultural and intellectual centre, noted for its library, second only to that in Alexandria, attracted both Stoic and Platonic philosophers, to whom Galen was exposed at age 14, his studies took in each of the principal philosophical systems of the time, including Aristotelian and Epicurean. His father had planned a traditional career for Galen in philosophy or politics and took care to expose him to literary and philosophical influences. However, Galen states that in around AD 145 his father had a dream in which the god Asclepius appeared and commanded Nicon to send his son to study medicine.
Again, no expense was spared, following his earlier liberal education, at 16 he began studies at the prestigious local sanctuary or Asclepieum dedicated to Asclepius, god of medicine, as a θεραπευτής for four years. There he came under the influence of men like Aeschrion of Pergamon and Satyrus. Asclepiea functioned as spas or sanitoria to which the sick would come to seek the ministrations of the priesthood. Romans frequented the temple at Pergamon in search of medical relief from disease, it was the haunt of notable people such as Claudius Charax the historian, Aelius Aristides the orator, Polemo the sophist, Cuspius Rufinus the Consul. Galen's father died in 148, leaving Galen independently wealthy at the age of 19, he followed the advice he found in Hippocrates' teaching and travelled and studied including such destinations as Smyrna, Crete, Cilicia and the great medical school of Alexandria, exposing himself to the various schools of thought in medicine. In 157, aged 28, he returned to Pergamon as physician to the gladiators of the High Priest of Asia, one of the most influential and wealt
The point where the upper temporal line cuts the coronal suture is named the stephanion. This article incorporates text in the public domain from page 183 of the 20th edition of Gray's Anatomy Item #22
An infratemporal fenestra called the lateral temporal fenestra is an opening in the skull behind the orbit in some animals. An opening in front of the eye sockets, conversely, is called an antorbital fenestra. Both of these openings reduced the weight of the skull. Infratemporal fenestrae are seen in the fossilized skulls of dinosaurs. Temporal fenestra
Facial symmetry is one specific measure of bodily asymmetry. Along with traits such as averageness and youthfulness it influences judgments of aesthetic traits of physical attractiveness and beauty. For instance, in mate selection, people have been shown to have a preference of symmetry; this is because it is seen an indicator of health and genetic fitness, but as holding adaptation qualities. Facial symmetry has been suggested as a possible physical manifestation of the'big-five' personality traits. For example, it is found that extraversion and openness are associated with the symmetry of the face. Hormones such as testosterone and estrogen are believed to be associated with developmental processes and growth of facial features during puberty and as a result are hypothesized to be the cause for individual differences in the implications associated with facial symmetry. Facial bilateral symmetry is measured via fluctuating asymmetry of the face comparing random differences in facial features of the two sides of the face that develop and accumulate throughout one's lifetime as a result of stressors.
Facial symmetry has been shown to have an effect of ratings of attractiveness in human faces. More symmetrical faces are perceived as more attractive in both males and females, although facial symmetry plays a larger role in judgments of attractiveness concerning female faces. A wide variety of methods have been used to examine the claim that facial symmetry plays a role in judgments of beauty. Blending of multiple faces to create a composite and face-half mirroring have been among the techniques used. While studies employing the first method produced results that indicate that more symmetrical faces are perceived as more attractive, studies applying the method have indicated that humans prefer slight asymmetry. Studies show that nearly symmetrical faces are considered attractive compared to unsymmetrical ones, yet more people tend to find a face unattractive if a person has an unsymmetrical nose, effect of unsymmetrical lips do not affect people on judging attractiveness; the most conspicuous directional asymmetries are sometimes only temporary.
For example, during speech, most people tend to express greater amplitude of movement on the right side of their mouth. This is most caused by the uneven strengths of contralateral neural connections between the left hemisphere of the brain and the right side of the face. Conclusions derived from face mirroring, have been called into question, because it has been shown that mirroring face-halves creates artificial features. For example, if the nose of an individual is bent to the right side mirroring the right side of the face will lead to an over-sized nose, while mirroring the left side will lead to an unnaturally small nose. Evolutionary theorists in biology and psychology argue that more symmetric faces are preferred because symmetry is a possible honest sign of superior genetic quality and developmental stability; however it is possible that high facial symmetry in an individual is not due to their superior genetics but due to a lack of exposure to stressors during development. This confounding source of facial symmetry is not explored in the literature.
The notion that facial symmetry is viewed by humans as an indicator of'good genes' is supported by experiments demonstrating that more symmetrical faces are rated as healthier than less symmetrical faces. For example, evidence has found that ratings of a person’s facial symmetry is positively associated with ratings of healthiness of their facial skin. Additionally, asymmetry can be fluctuated by increasing health challenges during growth; as a result, phenotypic quality and how well an individual's genome can fight disease and uphold normal development can be indicated by symmetry. Furthermore, studies suggest that facial fluctuation asymmetry, non symmetrical faces, may be associated with an individuals physiological and emotional distress. Additionally current studies indicate that face preferences in adults can be predicted by the number of infections in childhood. People who had more infections as children prefer more sex-typical and symmetric faces because those faces indicate being healthy.
Recent infections trigger this preference. Facial symmetry is a valid marker of cognitive aging. Progressive changes occurring throughout life in the soft tissues of the face will cause more prominent facial asymmetry in older faces. Therefore, symmetrical transformation of older faces increases their attractiveness while symmetrical transformation in young adults and children will decrease their attractiveness. Males with more symmetric faces in old age have higher intelligence and are more efficient at information processing than males with less symmetric faces; this is due to the better genes leading to more resistance against stressors in life, reflected in less accumulated fluctuating asymmetry. Non-scientific theories of attraction and symmetry abound. Symmetry of each face is evaluated by human brain via the facial recognition process; this fast and effective detection is difficult with computer programs. For instance, the faces that were considered to possess a strong aesthetic appeal were the ones where the conjunction of similar or corresponding facial features were, to some extent, contrasting.
Shared features echoism and similarity to people the person bonded to early in life have been suggested as relevant. Research indicates; the most consistent finding is that facial symmetry is positively correlated with extraversio
The temporal muscle known as the temporalis, is one of the muscles of mastication. It is a broad, fan-shaped muscle on each side of the head that fills the temporal fossa, superior to the zygomatic arch so it covers much of the temporal bone. In humans, it arises from the deep part of temporal fascia, it passes medial to the zygomatic arch and forms a tendon which inserts onto the coronoid process of the mandible, with its insertion extending into the retromolar fossa posterior to the most distal mandibular molar. In other mammals, the muscle spans the dorsal part of the skull all the way up to the medial line. There, it may be attached to a sagittal crest, as can be seen in early hominins like Paranthropus aethiopicus; the temporal muscle is covered by the temporal fascia known as the temporal aponeurosis. This fascia is used in tympanoplasty, or surgical reconstruction of the eardrum; the muscle is accessible on the temples, can be seen and felt contracting while the jaw is clenching and unclenching.
The temporalis is derived from the first pharyngeal arch in development. As with the other muscles of mastication, control of the temporal muscle comes from the third branch of the trigeminal nerve; the muscle is innervated by the deep temporal nerves. The muscle receives its blood supply from the deep temporal arteries which anastomose with the middle temporal artery; the temporal muscle is the most powerful muscle of the temporomandibular joint. The temporal muscle can be divided into two functional parts; the anterior portion its contraction results in elevation of the mandible. The posterior portion has fibers which run horizontally and contraction of this portion results in retrusion of the mandible; when lower dentures are fitted, they should not extend into the retromolar fossa to prevent trauma of the mucosa due to the contraction of the temporalis muscle. The temporalis is to be involved in jaw pain and headaches. Bruxism, the habitual grinding of teeth while sleeping, clenching of the jaw while stressed can lead to overwork of the temporalis and results in pain.
A myotendinous rupture of the temporalis can occur during a seizure due to extreme clenching of the jaw. During a seizure the contralateral temporalis muscle can enter spastic paralysis, this clenching in extreme cases can lead to a rupture on the myotendinous insertion at the coronoid process of the mandible. Anatomy photo:27:04-0100 at the SUNY Downstate Medical Center - "Infratemporal Fossa: The Temporalis Muscle" The anatomical basis for surgical preservation of temporal muscle, Kadri, et al. J Neurosurg 2004, 100:517–522 at http://www.mc.vanderbilt.edu/documents/singerlab/files/Kadri%20et%20al.pdf Temporalis Muscle Transfer, The Methodist Hospital System, Houston, TX, at http://www.methodistfacialparalysis.com/temporalis/