Week 2 Laboratory Materials PDF

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Week 2 Laboratory Materials...

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Teeth - Teeth are the only direct interface between the body’s hard tissues and the external environment. - Many features of the teeth are evolutionarily conservative, meaning that they reflect the ancestors of different groups of primates. - For this reason, anthropologists can look at the teeth of an unknown fossil primate to learn what its close relatives may be. - Teeth also reflect the dietary choices of different kinds of primates. - Sharp, pointy teeth are useful for piercing the hard exoskeletons of insects; - Teeth with high interlocking faces are good for cutting through tough leaves, - Teeth with flat grinding surfaces are useful for mashing and chewing hard items like seeds and nuts - Useful in understanding these aspects of primate relationships and behavior. - Working with the Jaw - Human teeth are arranged in an arch-shape around the jaw - Buccal: The side facing the cheek. The molars and premolars are sometimes called “cheek teeth” because they have a buccal side. - Labial: The side facing the lips. Incisors and canines, in the front of the mouth, have a labial side rather than a buccal side. - Lingual: The side facing the tongue. - Mesial: The side toward the front and center of the jaw. - Distal: The side around the dental arch toward the back of the jaw. - Occlusal: The surface that chews against the opposite jaw. - The human permanent dentition has four kinds of teeth. - We can divide the entire mouth into four quadrants. - Each quadrant is half of either the upper or lower jaw. - In humans each quadrant has the same number of teeth, and the same number of each type of teeth.

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Dental formula - Each quadrant in the human jaw has two incisors at the front, or mesial end, followed by a single canine, two premolars and three molars.

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- Many people, though, are missing one or more of these teeth. The two incisors, one canine, two premolars and three molars on both top and bottom are called the human dental formula. We write a dental formula as

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follows: - The numbers on the top refer to the maxillary dentition, the teeth of the upper jaw, and the numbers on the bottom refer to the mandibular dentition, in the lower jaw. Other kinds of primates have different dental formulas. - Platyrrhine monkeys and many lemurs have three premolars in each quadrant. - This is different from catarrhines, which only have two premolars. - With three premolars in each quadrant, most platyrrhines and

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strepsirrhines have a formula of Some branches within these primate groups differ from the larger group. - For example, many marmosets have only two permanent molars in each quadrant. - Occasionally, individuals may differ from the usual dental formula of their species. - People who are missing their third molars, for example, have a dental

formula of: Incisors - The incisors are the front teeth. They are basically flat and have a blade-like occlusal surface. Each quadrant has two incisors. - In humans and many other primates, the upper central incisor (called the I1) is typically larger, the lateral (the I2) smaller. The lower incisors (I1 and I2) are also flat and blade-like, and are much smaller in length than the upper incisors

Canines - The canine teeth in humans range from pointy-shaped to incisor-like in shape. - There is only one canine in each quadrant, and it is the third tooth just distal to the incisors.

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Upper canines are often denoted UC and lower canines are then LC (so that the left lower canine is LLC. - In many other primates, the canine teeth project out far beyond the others. - There is often a large space, or between the upper canine and the lateral incisor. - For many species, the canine teeth are the largest difference between male and female skulls. Premolars - The premolars are directly distal to (behind) the canines. - Humans generally have two premolars in each quadrant, the fourth and fifth teeth from the midline. - In anthropology, we number these teeth differently from dentists. - This is because the premolars in humans are homologous with the distal premolars in other mammals. - During the course of primate evolution, most primates lost the first premolar that many other mammals still retain. - Humans and other catarrhine primates share an ancestor that lost the second premolar also. - So anthropologists usually refer to human premolars as the third and fourth premolars, even though we have only two of them! The lowers are numbered P3and P4; the uppers P3 and P4. - Premolars usually have two distinct points, or cusps, on their occlusal surface. - In humans the lower third premolar is sometimes shaped very much like a canine tooth with only one cusp. - In many primates, the P3 has only one large cusp that cuts against the distal edge of the upper canine, like a scissors.

Molars - The most distal teeth are molars. - Most humans have three molars, but many — especially in America — have their third molars (called wisdom teeth) extracted. - Some people do not develop third molars at all, or they never erupt into occlusion.

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Molars have three or more cusps, and are used as grinding teeth. The upper molars are typically labeled with superscript numbers M1, M2, and M3, the lowers with subscript numbers M1, M2 and M3. - Hence, the left lower first molar becomes LM1.

Vertebrae and Shoulder Joint (Humans) -

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The vertebral column - The spine extends from the head to the sacrum, and in most people consists of 24 vertebrae. - Well, in most humans, anyway. Sometimes humans have a few more or less. - The human vertebral column can be divided into three segments: cervical, thoracic and lumbar. - Note that vertebrae is plural, while vertebra is singular. Each of the three segments of the spine has a curve. - The cervical and the lumbar curve both are convex anteriorly, while the thoracic spine curves the opposite way, convex posteriorly. - Each vertebra is shaped a bit like a wedge to support these curves, especially noticeable with the five lumbar vertebrae. - The lumbar curve is unique to humans, allowing us to maintain a vertical posture above our pelvis as we move bipedally.

Types of vertebrae -

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The cervical vertebrae are the first seven vertebrae, all in the neck. - These are smaller than the other vertebrae and lightly built. - There are two cervical vertebrae with unique features related to their special function. - The atlas is the first cervical vertebra. - It articulates with the base of the skull and allows the up and down, or "yes" motion, of the head. - The axis is the second cervical vertebra. - It has a boney process, or projection, around which the atlas can rotate. - This enables the head to move side to side in the "no" motion. There are twelve thoracic vertebrae, each articulating with the twelve pairs of ribs. - The lumbar vertebrae are the five lowest in the spine, between the ribs and the sacrum. - These have the largest vertebral bodies. - Humans vary in the length of the lumbar region. - The typical number is five, but some people have only four. Rarely, people have six lumbar vertebrae. Comparing primate spines - Primates have different numbers of vertebrae, sometimes more of one type or another. - This variation is connected to locomotion. - Species with vertical, suspensory postures have relatively short lumbar columns. - Chimpanzees, gorillas and orangutans have fewer lumbar vertebrae than humans.

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Quadrupedal primates, including most monkeys and prosimians, have longer lumbar columns than humans.

The schematic shows the spines of different kinds of primates - both New World and Old World monkeys and apes. - Do these primates vary in the other segments? Would they, for instance, have the same number of ribs? - As in humans, there is also variation between individuals in the number of vertebrae. One of the types of vertebrae does not vary across primates. Scapula - The length and orientation of the scapula is an important component of locomotion in primates and other mammals. - A relatively long and narrow scapula, oriented dorsally, will provide fast and powerful movement of the forelimb along the axis of the body, from front to back. - By contrast, a broader scapula, oriented more laterally, enables substantial movement of the arms beyond the front-to-back dimension.

The Lower Limb -

Femur - The femur is the bone of the upper leg. - The proximal end of the femur connects to the hip joint. - It is marked by a spherical ball, called the femoral head, that fits into the socket of the hip joint, the acetabulum. - The head is connected to the shaft of the femur by an elongated segment of

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bone, called the femoral neck. Lateral to the neck, a large projection juts proximally off the top of the bone, called the greater trochanter. A smaller projection on the posterior surface of the femur, just below the neck, is called the lesser trochanter. The shaft of the femur is thick, and may be quite straight or slightly curved from front to back. The distal end of the femur connects to the knee joint. It is marked by two large articular processes, called condyles, which sit on top of the tibia.

Tibia and fibula - The tibia and fibula are the bones of the lower leg. The fibula forms the lateral part of the ankle joint, preventing dislocation in that direction. - The tibia is much larger and thicker than the fibula. - On its proximal end, the tibia has two condyles that provide a platform on which the distal condyles of the femur sit during weight support. - The anterior surface of the tibia lies just under the skin, and is often called the shin. - At the proximal end of the anterior surface is the large tibial tuberosity, which most people can feel just below their kneecap. - The distal end of the tibia makes up much of the ankle joint, and the tibia has a distal projection on its medial side, called the medial malleolus, that can be felt on the inside surface of the ankle, and stabilizes the ankle in the medial direction.

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The tibial tuberosity is on the front, or anterior aspect, of the tibia, and the medial malleolus is medial. - These two features are good guides to determining whether a tibia is from the right or left side. - Remember, it is the skeleton’s right or left, not yours as you look at the bone.

The Upper Limb -

Humerus -

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The bone of the upper arm is called the humerus. It articulates with the scapula at the shoulder joint, and the radius and ulna at the elbow. - The proximal end of the humerus is dominated by a half-spherical articular surface, called the head, that forms the ball of the ball-andsocket joint of the shoulder. - The head points medially into the shoulder joint. - On the lateral side, a bump called the greater tubercle projects proximally. - The distal end of the humerus has two articular surfaces. - The first of these, called the trochlea, is a pulley-shaped surface that accommodates the ulna. - The other, called the capitulum, is a small spherical structure lateral to the trochlea that articulates with the head of the radius. - The capitulum is on the lateral side, the trochlea is medial. On the posterior surface, above the trochlea is a large dent, called the olecranon fossa. - The proximal end of the ulna fits into this fossa when the elbow is extended.

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Radius and ulna -

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The radius and ulna are the two bones of the lower arm. - Rotation of the wrist is actually accomplished by a rotation of the radius around the ulna. - The radius is on the lateral side of the arm, while the ulna is medial. The radius can turn at the elbow joint, and therefore the part of the radius that articulates with the humerus, called the radial head, has a rounded circumference that allows it to rotate in contact with the proximal ulna. - The radius has a large tuberosity on the front, toward the medial side. The proximal ulna has a large notch bounded by two bony processes. - The olecranon process fits into the olecranon fossa of the humerus, while the coronoid process fits against the anterior surface of the humerus when the elbow is flexed. - Between these two processes, a half-moon shaped notch, called the semilunar or trochlear notch, fits strongly around the trochlea of the humerus, creating a stable and strong hinge joint to counter the weak but rotating joint of the radius. - The proximal ulna has a notch for the radial head, called the radial notch, which is on the lateral side of the ulna. At the distal end, most of the proximal wrist joint is occupied by the distal radius, with the distal ulna free to rotate relative to the wrist. - Both bones have pointed styloid processes, which extend on the medial and lateral sides of the wrist....