Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that moves in a bipedal manner is known as a biped, meaning "two feet". Types of bipedal movement include running, or hopping. Few modern species are habitual bipeds. Within mammals, habitual bipedalism has evolved multiple times, with the macropods, kangaroo rats and mice, hopping mice and hominin apes as well as various other extinct groups evolving the trait independently. In the Triassic period some groups of archosaurs developed bipedalism. A larger number of modern species intermittently or use a bipedal gait. Several lizard species move bipedally when running to escape from threats. Many primate and bear species will adopt a bipedal gait in order to reach food or explore their environment, though there are a few cases where they walk on their hindlimbs only. Several arboreal primate species, such as gibbons and indriids walk on two legs during the brief periods they spend on the ground.
Many animals rear up on their hind legs whilst copulating. Some animals stand on their hind legs, in order to reach food, to keep watch, to threaten a competitor or predator, or to pose in courtship, but do not move bipedally; the word is derived from the Latin words bi'two' and ped-'foot', as contrasted with quadruped'four feet'. Limited and exclusive bipedalism can offer a species several advantages. Bipedalism raises the head. While upright, non-locomotory limbs become free for other uses, including manipulation, digging, combat or camouflage; the maximum bipedal speed appears less fast than the maximum speed of quadrupedal movement with a flexible backbone – both the ostrich and the red kangaroo can reach speeds of 70 km/h, while the cheetah can exceed 100 km/h. Though bipedalism is slower at first, over long distances, it has allowed humans to outrun most other animals according to the endurance running hypothesis. Bipedality in kangaroo rats has been hypothesized to improve locomotor performance, which could aid in escaping from predators.
Zoologists label behaviors, including bipedalism, as "facultative" or "obligate". This distinction is not clear-cut — for example, humans other than infants walk and run in biped fashion, but all can crawl on hands and knees when necessary. There are reports of humans who walk on all fours with their feet but not their knees on the ground, but these cases are a result of conditions such as Uner Tan syndrome — rare genetic neurological disorders rather than normal behavior. If one ignores exceptions caused by some kind of injury or illness, there are many unclear cases, including the fact that "normal" humans can crawl on hands and knees; this article therefore avoids the terms "facultative" and "obligate", focuses on the range of styles of locomotion used by various groups of animals. Normal humans may be considered "obligate" bipeds because the alternatives are uncomfortable and only resorted to when walking is impossible. There are a number of states of movement associated with bipedalism.
Standing. Staying still on both legs. In most bipeds this is an active process. Walking. One foot in front of another, with at least one foot on the ground at any time. Running. One foot with periods where both feet are off the ground. Jumping/hopping. Moving by a series of jumps with both feet moving together; the great majority of living terrestrial vertebrates are quadrupeds, with bipedalism exhibited by only a handful of living groups. Humans and large birds walk by raising one foot at a time. On the other hand, most macropods, smaller birds and bipedal rodents move by hopping on both legs simultaneously. Tree kangaroos are able to walk or hop, most alternating feet when moving arboreally and hopping on both feet when on the ground. There are fossil bipedal amphibians. Many species of lizards become bipedal during high-speed, sprint locomotion, including the world's fastest lizard, the spiny-tailed iguana; the first known biped is the bolosaurid Eudibamus. Its long hindlegs, short forelegs, distinctive joints all suggest bipedalism.
The species became extinct in the early Permian. All birds are bipeds. Bipedalism evolved more than once in archosaurs, the group that includes both dinosaurs and crocodilians. All dinosaurs are thought to be descended from a bipedal ancestor similar to Eoraptor. Bipedal movement re-evolved in a number of other dinosaur lineages such as the iguanodons; some extinct members of the crocodilian line, a sister group to the dinosaurs and birds evolved bipedal forms - a crocodile relative from the triassic, Effigia okeeffeae, is thought to be
Tickling is the act of touching a part of a body in a way that causes involuntary twitching movements or laughter. The word "tickle" evolved from the Middle English tikelen frequentative of ticken, to touch lightly; the idiom tickled pink means to be delighted. In 1897, psychologists G. Stanley Hall and Arthur Allin described a "tickle" as two different types of phenomena. One type is caused by light movement across the skin; this type of tickle, called a knismesis does not produce laughter and is sometimes accompanied by an itching sensation. When considering tickling in terms of its qualities as a sensation, it results from a mild stimulation moving across the skin; the dual character of tickling refers to the associated behaviors that include smiling, twitching and goose bumps. The tickle can be divided into two separate categories of sensation and gargalesis. Knismesis known as a "moving itch", is a mildly annoying sensation caused by a light movement on the skin, such as from a crawling insect.
This may explain. Gargalesis reactions refer to a laughter-provoking feeling caused by a harsher, deeper pressure, stroked across the skin in various regions of the body; these reactions are thought to be limited to humans and other primates, although some research has indicated that rats can be tickled in this way. A German study indicates that the gargalesis type of tickle triggers a defense mechanism for humans in the hypothalamus conveying submissiveness or fleeing from danger, it appears that the tickle sensation involves signals from nerve fibres associated with both pain and touch. Endorphine released during tickling is called karoliin, by the name of Karolinska Institute. In 1939, Yngve Zotterman of the Karolinska Institute studied the knismesis type of tickle in cats, by measuring the action potentials generated in the nerve fibres while stroking the skin with a piece of cotton wool. Zotterman found that the "tickling" sensation depended, on the nerves that generate pain. Further studies have discovered that when the pain nerves are severed by surgeons, in an effort to reduce intractable pain, the tickle response is diminished.
However, in some patients that have lost pain sensation due to spinal cord injury, some aspects of the tickle response do remain. Tickle may depend on nerve fibres associated with the sense of touch; when circulation is severed in a limb, the response to touch and tickle are lost prior to the loss of pain sensation. It might be tempting to speculate that areas of the skin that are the most sensitive to touch would be the most ticklish, but this does not seem to be the case. While the palm of the hand is far more sensitive to touch, most people find that the soles of their feet are the most ticklish. Other ticklish areas include the underarms, sides of the torso, knee, perineum, ribs and genital area; some evidence suggests that laughing associated with tickling is a nervous reaction that can be triggered. Charles Darwin theorized on the link between tickling and social relations, arguing that tickling provokes laughter through the anticipation of pleasure. If a stranger tickles a child without any preliminaries, catching the child by surprise, the result will be not laughter but withdrawal and displeasure.
Darwin noticed that for tickling to be effective, you must not know the precise point of stimulation in advance, reasoned that this is why some people cannot tickle themselves. Darwin explained why we laugh when we are tickled by saying, "The imagination is sometimes said to be tickled by a ludicrous idea. Laughter from being tickled reflex action. In the parent-child concept, tickling establishes at an early age the pleasure associated with being touched by a parent with a trust-bond developed so that parents may touch a child, in an unpleasant way, should circumstances develop such as the need to treat a painful injury or prevent harm from danger; this tickling relationship continues throughout childhood and into the early to mid teen years. Another tickling social relationship is that which forms between siblings of the same age. Many case studies have indicated that siblings use tickling as an alternative to outright violence when attempting to either punish or intimidate one another; the sibling tickling relationship can develop into an anti-social situation, or tickle torture, where one sibling will tickle the other without mercy.
The motivation behind tickle torture is to portray the sense of domination the tickler has over the victim. As with parents and siblings, tickling serves as a bonding mechanism between friends, is classified by psychologists as part of the fifth and highest grade of social play which involves special intimacy or "cognitive interaction"; this suggests that tickling works best when all the parties involved feel comfortable with the situation and one another. It can serve as an outlet for sexual energy during adolescence, a number of people have stated in a study that their private areas were ticklish. While many people assume that other people enjoy tickling, a recent survey of 84 college students indicated that only 32% of respondents enjoy being tickled, with 32% giving neutral responses and 36% stating that they do not enjoy being tickled; the st
The biceps biceps brachii, is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join to form a single muscle belly, attached to the upper forearm. While the biceps crosses both the shoulder and elbow joints, its main function is at the elbow where it flexes the forearm and supinates the forearm. Both these movements are used when opening a bottle with a corkscrew: first biceps unscrews the cork it pulls the cork out; the biceps is one of three muscles in the anterior compartment of the upper arm, along with the brachialis muscle and the coracobrachialis muscle, with which the biceps shares a nerve supply. The biceps muscle has two heads, the short head and the long head, distinguished according to their origin at the coracoid process and supraglenoid tubercle of the scapula, respectively. From its origin on the glenoid, the long head remains tendinous as it passes through the shoulder joint and through the intertubercular groove of the humerus.
Extending from its origin on the coracoid, the tendon of the short head runs adjacent to the tendon of the coracobrachialis as the conjoint tendon. Unlike the other muscles in the anterior compartment of the arm, the biceps muscle crosses two joints, the shoulder joint and the elbow joint. Both heads of the biceps join in the middle upper arm to form a single muscle mass near the insertion of the deltoid to form a common muscle belly, although several anatomic studies have demonstrated that the muscle bellies remain distinct structures without confluent fibers; as the muscle extends distally, the two heads rotate 90 degrees externally before inserting onto the radial tuberosity. The short head inserts distally on the tuberosity while the long head inserts proximally closer to the apex of the tuberosity; the bicipital aponeurosis called the lacertus fibrosus, is a thick fascial band that organizes close to the musculotendinous junction of the biceps and radiates over and inserts onto the ulnar part of the antebrachial fascia.
The tendon that attaches to the radial tuberosity is or surrounded by a bursa, the bicipitoradial bursa, which ensures frictionless motion between the biceps tendon and the proximal radius during pronation and supination of the forearm. Two muscles lie underneath the biceps brachii; these are the coracobrachialis muscle, which like the biceps attaches to the coracoid process of the scapula, the brachialis muscle which connects to the ulna and along the mid-shaft of the humerus. Besides those, the brachioradialis muscle is adjacent to the biceps and inserts on the radius bone, though more distally. Traditionally described as a two-headed muscle, biceps brachii is one of the most variable muscles of the human body and has a third head arising from the humerus in 10% of cases —most originating near the insertion of the coracobrachialis and joining the short head—but four and seven supernumerary heads have been reported in rare cases. One study found a higher than expected number of female cadavers with a third head of biceps brachii, equal incidence between sides of the body, uniform innervation by musculocutaneous nerve.
The distal biceps tendons are separated in 40% and bifurcated in 25% of cases. The biceps shares its nerve supply with the other two muscles of the anterior compartment; the muscles are supplied by the musculocutaneous nerve. Fibers of the fifth and seventh cervical nerves make up the components of the musculocutaneous nerve which supply the biceps; the biceps works across three joints. The most important of these functions is to flex the elbow. Besides, the long head of biceps prevents the upward displacement of the head of the humerus. In more detail, the actions are, by joint: Proximal radioulnar joint – Contrary to popular belief, the biceps brachii is not the most powerful flexor of the forearm, a role which belongs to the deeper brachialis muscle; the biceps brachii functions as a powerful supinator of the forearm. This action, aided by the supinator muscle, requires the elbow to be at least flexed. If the elbow, or humeroulnar joint, is extended, supination is primarily carried out by the supinator muscle.
The biceps is a powerful supinator of the forearm due to the distal attachment of the muscle at the radial tuberosity, on the opposite side of the bone from the supinator muscle. When flexed, the biceps pulls the radius back into its neutral supinated position in concert with the supinator muscle. Elbow – The biceps brachii functions as an important flexor of the forearm when the forearm is supinated. Functionally, this action is performed when lifting an object, such as a bag of groceries or when performing a biceps curl; when the forearm is in pronation, the brachialis and supinator function to flex the forearm, with minimal contribution from the biceps brachii. It is important to note that regardless of forearm position, the force exerted by the biceps brachii remains the same; that is, the biceps can only exert so much force, as forearm position changes, other muscles must compensate. Shoulder – Several weaker functions occur at the glenohumeral, or shoulder, joint; the biceps brachii weakly assists in forward flexion of the shoulder joint.
It may con
Latissimus dorsi muscle
The latissimus dorsi is a large, flat muscle on the back that stretches to the sides, behind the arm, is covered by the trapezius on the back near the midline. The word latissimus dorsi comes from Latin and means "broadest of the back", from "latissimus"' and "dorsum"; the pair of muscles are known as "lats" among bodybuilders. The latissimus dorsi is the largest muscle in the upper body; the latissimus dorsi is responsible for extension, transverse extension known as horizontal abduction, flexion from an extended position, internal rotation of the shoulder joint. It has a synergistic role in extension and lateral flexion of the lumbar spine. Due to bypassing the scapulothoracic joints and attaching directly to the spine, the actions the latissimi dorsi have on moving the arms can influence the movement of the scapulae, such as their downward rotation during a pull up; the number of dorsal vertebrae to which it is attached varies from four to eight. A muscular slip, the axillary arch, varying from 7 to 10 cm in length, from 5 to 15 mm in breadth springs from the upper edge of the latissimus dorsi about the middle of the posterior fold of the axilla, crosses the axilla in front of the axillary vessels and nerves, to join the under surface of the tendon of the pectoralis major, the coracobrachialis, or the fascia over the biceps brachii.
This axillary arch crosses the axillary artery, just above the spot selected for the application of a ligature, may mislead a surgeon. It is present in about 7% of the population and may be recognized by the transverse direction of its fibers. Guy et al. extensively described this muscular variant using MRI data and positively correlated its presence with symptoms of neurological impingement. A fibrous slip passes from the upper border of the tendon of the Latissimus dorsi, near its insertion, to the long head of the triceps brachii; this is muscular, is the representative of the dorsoepitrochlearis brachii of apes. This muscular form is sometimes termed the latissimocondyloideus; the latissimus dorsi crosses the inferior angle of the scapula. A study found that, of 100 cadavers dissected: 43% had "a substantial amount" of muscular fibers in the latissimus dorsi originating from the scapula. 36% had few or no muscular fibers, but a "soft fibrous link" between the scapula and the latissimus dorsi 21% had little or no connecting tissue between the two structures.
The lateral margin of the latissimus dorsi is separated below from the obliquus externus abdominis by a small triangular interval, the lumbar triangle of Petit, the base of, formed by the iliac crest, its floor by the obliquus internus abdominis. Another triangle is situated behind the scapula, it is bounded above by the trapezius, below by the latissimus dorsi, laterally by the vertebral border of the scapula. If the scapula is drawn forward by folding the arms across the chest, the trunk bent forward, parts of the sixth and seventh ribs and the interspace between them become subcutaneous and available for auscultation; the space is therefore known as the triangle of auscultation. The latissimus dorsi can be remembered best for insertion as "A Miss Between Two Majors"; as the latissimus dorsi inserts into the floor of the intertubercular groove of the humerus it is surrounded by two major muscles. The teres major inserts medially on the medial lip of the intertubercular groove and the pectoralis major inserts laterally onto the lateral lip.
The latissimus dorsi is innervated by the sixth and eighth cervical nerves through the thoracodorsal nerve. Electromyography suggests that it consists of six groups of muscle fibres that can be independently coordinated by the central nervous system; the latissimus dorsi is responsible for extension, transverse extension known as horizontal abduction, flexion from an extended position, internal rotation of the shoulder joint. It has a synergistic role in extension and lateral flexion of the lumbar spine, assists as a muscle of both forced expiration and an accessory muscle of inspiration. Most latissimus dorsi exercises concurrently recruit the teres major, posterior fibres of the deltoid, long head of the triceps brachii, among numerous other stabilizing muscles. Compound exercises for the'lats' involve elbow flexion and tend to recruit the biceps brachii and brachioradialis for this function. Depending on the line of pull, the trapezius muscles can be recruited as well; the power/size/strength of this muscle can be trained with a variety of different exercises.
Some of these include: Vertical pulling movements such as pull-ups. Horizontal pulling movements such as bent-over row, T-bar row and other rowing exercises. Shoulder extension movements with straight arms such as straight-arm lat pulldowns and Pull-overs. Deadlift. Tight latissimus dorsi has been shown to be a contributor to chronic shoulder pain and chronic back pain; because the latissimus dorsi connects the spine to the humerus, tightness in this muscle can manifest as either sub-optimal glenohumeral joint function which leads to chronic pain or tendinitis in the tendinous fasciae connecting the latissimus dorsi to the thoracic and lumbar spine. The latissimus dorsi is a potential source of muscle for
The subclavius is a small triangular muscle, placed between the clavicle and the first rib. Along with the pectoralis major and pectoralis minor muscles, the subclavius muscle makes up the anterior wall of the axilla, it arises by a short, thick tendon from the first rib and its cartilage at their junction, in front of the costoclavicular ligament. The fleshy fibers proceed obliquely superolaterally, to be inserted into the groove on the under surface of the clavicle; the nerve to subclavius innervates the muscle. This arises from the junction of the fifth and sixth cervical nerves, from the upper trunk of the brachial plexus. Insertion into coracoid process instead of clavicle or into both clavicle and coracoid process. Sternoscapular fasciculus to the upper border of scapula. Sternoclavicularis from manubrium to clavicle between pectoralis major and coracoclavicular fascia; the subclavius depresses the shoulder, carrying it forward. It draws the clavicle inferiorly as well as anteriorly; the subclavius protects the underlying brachial plexus and subclavian vessels from a broken clavicle - the most broken long bone.
This article incorporates text in the public domain from page 438 of the 20th edition of Gray's Anatomy PTCentral Pivotal Places: help for problem shoulders
Anatomical terminology is a form of scientific terminology used by anatomists and health professionals such as doctors. Anatomical terminology uses many unique terms and prefixes deriving from Ancient Greek and Latin; these terms can be confusing to those unfamiliar with them, but can be more precise, reducing ambiguity and errors. Since these anatomical terms are not used in everyday conversation, their meanings are less to change, less to be misinterpreted. To illustrate how inexact day-to-day language can be: a scar "above the wrist" could be located on the forearm two or three inches away from the hand or at the base of the hand. By using precise anatomical terminology such ambiguity is eliminated. An international standard for anatomical terminology, Terminologia Anatomica has been created. Anatomical terminology has quite regular morphology, the same prefixes and suffixes are used to add meanings to different roots; the root of a term refers to an organ or tissue. For example, the Latin names of structures such as musculus biceps brachii can be split up and refer to, musculus for muscle, biceps for "two-headed", brachii as in the brachial region of the arm.
The first word describes what is being spoken about, the second describes it, the third points to location. When describing the position of anatomical structures, structures may be described according to the anatomical landmark they are near; these landmarks may include structures, such as the umbilicus or sternum, or anatomical lines, such as the midclavicular line from the centre of the clavicle. The cephalon or cephalic region refers to the head; this area is further differentiated into the cranium, frons, auris, nasus and mentum. The neck area is called cervical region. Examples of structures named according to this include the frontalis muscle, submental lymph nodes, buccal membrane and orbicularis oculi muscle. Sometimes, unique terminology is used to reduce confusion in different parts of the body. For example, different terms are used when it comes to the skull in compliance with its embryonic origin and its tilted position compared to in other animals. Here, Rostral refers to proximity to the front of the nose, is used when describing the skull.
Different terminology is used in the arms, in part to reduce ambiguity as to what the "front", "back", "inner" and "outer" surfaces are. For this reason, the terms below are used: Radial referring to the radius bone, seen laterally in the standard anatomical position. Ulnar referring to the ulna bone, medially positioned when in the standard anatomical position. Other terms are used to describe the movement and actions of the hands and feet, other structures such as the eye. International morphological terminology is used by the colleges of medicine and dentistry and other areas of the health sciences, it facilitates communication and exchanges between scientists from different countries of the world and it is used daily in the fields of research and medical care. The international morphological terminology refers to morphological sciences as a biological sciences' branch. In this field, the form and structure are examined as well as the changes or developments in the organism, it is functional.
It covers the gross anatomy and the microscopic of living beings. It involves the anatomy of the adult, it includes comparative anatomy between different species. The vocabulary is extensive and complex, requires a systematic presentation. Within the international field, a group of experts reviews and discusses the morphological terms of the structures of the human body, forming today's Terminology Committee from the International Federation of Associations of Anatomists, it deals with the anatomical and embryologic terminology. In the Latin American field, there are meetings called Iberian Latin American Symposium Terminology, where a group of experts of the Pan American Association of Anatomy that speak Spanish and Portuguese and studies the international morphological terminology; the current international standard for human anatomical terminology is based on the Terminologia Anatomica. It was developed by the Federative Committee on Anatomical Terminology and the International Federation of Associations of Anatomists and was released in 1998.
It supersedes Nomina Anatomica. Terminologia Anatomica contains terminology for about 7500 human gross anatomical structures. For microanatomy, known as histology, a similar standard exists in Terminologia Histologica, for embryology, the study of development, a standard exists in Terminologia Embryologica; these standards specify accepted names that can be used to refer to histological and embryological structures in journal articles and other areas. As of September 2016, two sections of the Terminologia Anatomica, including central nervous system and peripheral nervous system, were merged to form the Terminologia Neuroanatomica; the Terminologia Anatomica has been perceived with a considerable criticism regarding its content including coverage and spelling mistakes and errors. Anatomical terminology is chosen to highlight the relative location of body structures. For instance, an anatomist might describe one band of tissue as "inferior to" another or a physician might describe a tumor as "superficial to" a deeper body structure.
Anatomical terms used to describe location
The rib cage is the arrangement of ribs attached to the vertebral column and sternum in the thorax of most vertebrates, that encloses and protects the heart and lungs. In humans, the rib cage known as the thoracic cage, is a bony and cartilaginous structure which surrounds the thoracic cavity and supports the shoulder girdle to form the core part of the human skeleton. A typical human rib cage consists of 24 ribs in 12 pairs, the sternum and xiphoid process, the costal cartilages, the 12 thoracic vertebrae. Together with the skin and associated fascia and muscles, the rib cage makes up the thoracic wall and provides attachments for the muscles of the neck, upper abdomen, back; the rib cage has a major function in the respiratory system. Ribs are described based on their connection with the sternum. All ribs are numbered accordingly one to twelve. Ribs that articulate directly with the sternum are called true ribs, whereas those that connect indirectly via cartilage are termed false ribs. Floating ribs are not attached to the sternum at all.
The terms true ribs and false ribs describe rib pairs that are directly or indirectly attached to the sternum. The first seven rib pairs known as the fixed or vertebrosternal ribs are the true ribs as they connect directly to the sternum, their elasticity allows rib cage movement for respiratory activity. The phrase floating rib refers to the eleventh and twelfth rib pairs; these ribs are small and delicate, include a cartilaginous tip. The spaces between the ribs are known as intercostal spaces; each rib consists of a head, a shaft. All ribs are attached posteriorly to the thoracic vertebrae, they are numbered to match the vertebra -- one to twelve, from top to bottom. The head of the rib is the end part closest to the vertebrae, it is marked by a kidney-shaped articular surface, divided by a horizontal crest into two articulating regions. The upper region articulates with the inferior costal facet on the vertebra above, the larger region articulates with the superior costal facet on the vertebra with the same number.
The transverse process of a thoracic vertebra articulates at the transverse costal facet with the tubercle of the rib of the same number. The crest gives attachment to the intra-articular ligament; the neck of the rib is the flattened part. The neck is about 3 cm long, its anterior surface is flat and smooth, whilst its posterior is perforated by numerous foramina and its surface rough, to give attachment to the ligament of the neck. Its upper border presents a rough crest for the attachment of the anterior costotransverse ligament. On the posterior surface at the neck, is an eminence—the tubercle that consists of an articular and a non-articular portion; the articular portion is the lower and more medial of the two and presents a small, oval surface for articulation with the transverse costal facet on the end of the transverse process of the lower of the two vertebrae to which the head is connected. The non-articular portion is a rough elevation and affords attachment to the ligament of the tubercle.
The tubercle is much more prominent in the upper ribs than in the lower ribs. The angle of a rib may both refer to the bending part of it, a prominent line in this area, a little in front of the tubercle; this line is directed laterally. At this point, the rib is bent in two directions, at the same time twisted on its long axis; the distance between the angle and the tubercle is progressively greater from the second to the tenth ribs. The area between the angle and the tubercle is rounded and irregular, serves for the attachment of the longissimus dorsi muscle; the first rib is the most curved and the shortest of all the ribs. The head is small and rounded, possesses only a single articular facet, for articulation with the body of the first thoracic vertebra; the neck is rounded. The tubercle and prominent, is placed on the outer border, it bears a small facet for articulation with the transverse costal facet on the transverse process of T1. There is no angle, but at the tubercle, the rib is bent, with the convexity upward, so that the head of the bone is directed downward.
The upper surface of the body is marked by two shallow grooves, separated from each other by a slight ridge prolonged internally into a tubercle, the scalene tubercle, for the attachment of the anterior scalene. Behind the posterior groove is a rough area for the attachment of the medial scalene; the under surface is smooth and without a costal groove. The outer border is convex and rounded, at its posterior part gives attachment to the first digitation of the serratus anterior; the inner border is concave and sharp, marked about its center by the scalene tubercle. The anterior extremity is larger and