MUSCLE TISSUE (Part 2)

superior and inferior assist the superior and inferior recti to turn the eye-ball downward, inward, or outward, and upward, outward, or inward. The internal and external recti also assist in these complicated actions of the eyes. THE MUSCLES OF THE HEAD AND NECK 129 Nerve Supply. — ^All supplied by the motor oculi or third cranial nerve, except the external rectus, and it is innervated by the abducent or sixth cranial nerve; the superior oblique is supplied by the trochlear or fourth cranial nerve. The Muscles of the Nose (Nasal Region) Pyramidalis nasi. Dilator naris anterior. Levator labii superioris Compressor nasi. alseque nasi. Compressor narium minor. Dilator naris posterior. Depressor alse nasi. The above muscles are just beneath the skin and fascia and most of them are inserted into the skin; they arise from the bones, fascia, and cartilages. The Muscles of the Cheeks and Lips (Maxillary Region) Levator labii superioris. Zygomaticus major. Levator anguli oris. Zygomaticus minor. The Levator Labii Superioris. — Origin, lower margin of orbit, some fibers from maxilla and malar bones, insertion into muscular portion of upper lip. Action — elevates and assists in protruding the upper lip. Nerve, facial. The Levator Anguli Oris. — Origin, canine fossa of maxilla; inserted into skin and fascia near angle of mouth, blending with the fibers of the zygomaticus major, depressor anguli oris, and orbicularis oris. Action — elevates angle of mouth. Nerve, facial. Zygomaticus Major. — Origin, malar bone; inserted into skin and fascia outer portion of upper lip and angle of mouth, blending with the fibers of the levator anguli oris, orbicularis oris, and the depressor anguli oris. Action — draws the angle of the mouth upward and backward, as in laughing. Nerve, facial. 9 130 MUSCLE TISSUE Zygomaticus Minor. — Origin, malar bone; inserted into skin and fascia of upper lip internal to angle of mouth and the insertion of the zygomaticus major; fuses with jSbers of orbicularis oris. Action — draws the upper lip backward, upward, and outward, thus gives to the face an expression of sadness. Nerve, facial. The Muscles of the Chin and Lower Lip (Mandibular Region) Levator menti. Depressor anguli oris. Depressor labii inferioris. Levator Menti. — Origin, mandible external to sym- physis; inserted into skin of chin. Action — ^raises lower lip, wrinkles chin, gives to the face the expression of doubt, disdain, and pouting. Nerve, facial. Depressor Anguli Oris. — Origin, from mandible, in- serted into angle of mouth. It is blended with the platysma, orbicularis oris, risorius, and levator anguli oris. Action — depresses angle of mouth. Acting with the levator anguli oris the two will depress angles of the mouth directly inward, as in smirking. Nerve, facial. Depressor Labii Inferioris. — Origin from mandible; insertion, skin of lower lip, blends with fibers of orbicu- laris oris and muscle of opposite side. Action depresses lower lip. Nerve, facial. The Muscles of the Buccal Region Orbicularis oris. Buccinator. Risorius. Orbicularis Oris. — This is the muscle of the mouth and lips. It consists of oblique and transverse fibers THE MUSCLES OF THE HEAD AND NECK 131 which are not distinct, but fuse with the muscles in- serted into the skin and mucous membrane surround- ing the mouth. The buccinator muscle divides at the angle, and the fibers pass into the upper and lower part of the orbicularis oris; also at the angle entering from above are the fibers of the levator anguli oris, and from below the fibers of the depressor anguli oris. In addition to the former muscles crossing at the angle, are the fibers of the risorius which divide and blend with the upper and lower lips respectively. The other muscles inserted into the lips are: above, levator labii superioris (elevator of upper lip); levator labii supe- riors alaeque nasi (elevator of the upper lip and wing of the nose); the zygomaticus major and minor; and depressor labii inferioris (depressor of the lower lip). Actions are numerous and various, and only the ordi- nary or chief actions will be mentioned, as the muscles inserted into the orbicularis oris all aid it in the com- plex movements of this important muscle of expression. When the fibers contract they close the lips; the crossed fibers consisting of the superficial set brings the lips together and also protrudes them as in whistling, pouting, etc., the deep fibers assisted by the oblique fibers forcibly close the lips and hold them against the teeth — as when one refuses to take food or medicine by mouth. Nerve — facial. Buccinator. — This is the chief muscle of the cheek, and encloses the space between the two jaw bones. It is thus quadrilateral in shape. Arises from the alve- olar processes of the maxillag and mandible, behind from a thickened fibrous band, called the pterygomandibular ligament. The fibers come together at the angle of the mouth and pass to the upper and lower lips. Action — it is essentially a muscle of mastication. The muscle contracts the cheeks and compresses them so that the food during mastication is kept within the bounds of the teeth and comes in contact with their chewing 132 MUSCLE TISSUE or grinding action. When the cheeks are distended with air, the muscle contracts and expels it through the lips as in playing the cornet, flute, etc. Nerve — facial. Risorius. — A small thin muscle arises from the fascia over the masseter muscle, inserted into muscular and subcutaneous tissue at the angle of the mouth. Action. — Draws back the angle of the mouth as seen in lockjaw, giving the peculiar expression to the face known as the "sardonic grin or laugh;" also (both sides) assists in retracting angles of mouth as in smiling, associated with the other muscles at the angle. Nerve — facial. Muscles of Mastication Temporomandibular region. Pterygomandibular region. Masseter. External Pterygoid. Temporal. Internal Pterygoid. The muscles of mastication aid in preparing the food so that it can be easily swallowed. They bring the jaws together, so that the teeth approximate and chew, or by a lateral motion, grind the food. The Muscles of the Tongue (Lingual Region) The muscles of the tongue are divided into extrinsic, those situated outside of the organ, yet are inserted into it; and intrinsic, those contained within the organ, forming its substance. The Extrinsic Muscles. — ^These are: geniohyoglossus, hyoglossus, styloglossus, palatoglossus, and chondroglossus. The Intrinsic Muscles. — ^These are a series of inter- lacing fibers making up the substance of the tongue and are named according to their position and direc- tion, called lingualis, presenting — superior, inferior. THE MUSCLES OF THE HEAD AND NECK 133 transverse, and vertical fibers, with a medium fibrous septum. They all receive fibers from the extrinsic muscles at their points of insertion into the tongue. The Muscles of the Soft Palate (Palatal Region) The soft palate is continued back from the hard palate, and is seen on opening the mouth as an arch with a central projection called the uvula, directly over the back of the tongue. Beneath the mucous membrane covering these parts are the muscles of the soft palate, as follows: Levator palati. Palatoglossus. Tensor palati. Palatopharyngeus. Azygos uvulse. Salpingopharyngeus. The Muscles of the Pharynx (Pharyngeal Region) Superior constrictor. Inferior constrictor. Middle constrictor. Stylopharyngeus. These muscles are divided into two layers — an outer flat and thin one — called the constrictors, with a transverse set of fibers; an inner — called the elevators, two in number, with a longitudinal arrangement of the fibers. Actions of pharyngeal muscles. Their chief function is to assist in swallowing the food after it has been masticated and forced into the pharynx by the tongue and muscles of the soft palate. At the beginning of deglutition the sides of the pharynx are raised upward and outward by the two stylopharyngei muscles, at the same time the larynx and tongue are carried forward. When the bolus of food is being received into the pharynx, the elevator muscles relax and the 134 MUSCLE TISSUE constrictor muscles contract upon the mass and force it into the esophagus. Fia. 64 Muscles of the pharynx. External view. (Gray.) The Muscles and Fasciae of the Neck The neck muscles are divided into a superficial and a deep set. They are arranged vertically and only the anterior or superficial set will be described, as the others are not important so far as the nurse^s knowledge is concerned. THE MUSCLES OF THE HEAD AND NECK 135 The Anterior Neck Muscles. — The platysma is a thin, pale muscle, extending over the front and sides of the neck, the lower region of the face, and as low as the Fia. 65 Muscles of the neck and boundaries of the triangles. (Gray.) upper aspect of the chest, just below the clavicles. It is just beneath the skin, invested by the superficial fascia, and above the deep cervical fascia of the neck. There are two such muscles. 136 MUSCLE TISSUE The Steraomastoid. — Origin, from anterior surface of the sternum, inner third of upper surface of clavicle; two portions meet and pass obliquely upward and back across the lateral aspect of the neck to be inserted into the anterior border and outer surface of the mastoid portion of the temporal bone. Actions. — ^The two muscles acting together bend the head upon the neck. When only one muscle contracts the head is drawn toward the shoulder of the same side, at the same time the head is rotated, so that the face is carried to the opposite side. When the head is held firm by the other muscles the sternomastoid acts as a muscle of respiration in forced breathing. Nerve — spinal accessory and deep branches of cervical plexus. Depressors of the Hyoid Bone Sternohyoid . Thyrohyoid . Sternothyroid. Omohyoid. The Elevators of the Hyoid Bone These muscles are situated at the inferior and lateral aspect of the floor of the mouth, below the mandible. They are covered by the deep cervical fascia of the neck. Digastric. Mylohyoid. Stylohyoid. Geniohyoid. Deep Neck Muscles There are numerous neck muscles deeply located in the neck; they assist to maintain the head erect and also aid in flexing, extending, and rotating the head on the spinal column. A description of these muscles will not be given, as they cannot be properly understood THE MUSCLES AND FASCIA OF THE TRUNK 137 unless seen, either in a diagram, or the human body. Other muscles arising froni the cervical vertebrae pass to the ribs and aid in forced inspiration and expiration ; still others posteriorly pass to the scapulae and thoracic vertebrae and assist in shrugging the shoulders, flexing and extending spinal column, rotating the vertebrae, etc. THE MUSCLES AND FASCIiE OF THE TRUNK In speaking of the trunk we include that part of the human body consisting of the back, thorax, abdomen, and perineal region. The Muscles of the Neck and Back The muscles of these regions are in layers, their actions and relations are too complex to include here except the ones described below. It is suflScient to state that they consist of five layers, in which are thirty-two or more pairs of muscles. These muscles are covered by a superficial fascia which is continuous with the fascia over the rest of the body; and a deep fascia, which is thick and fibrous, and curves over and forms sheaths for the muscles, being attached to the following bony prominences: occipital bone, crest of ilium, spines of vertebrae, and the spines of the scap- ulae. In the neck it forms the posterior portion of the deep cervical fascia, in the thorax blends with the axillary fascia and deep fascia of the thorax; it is continuous with the abdominal fascia, also forms the back layer of the lumbar fascia, and covers the erector spinae mass of muscles. The Trapezius. — This is the muscle situated at the back of the neck and shoulders. There are two. Origin, inner third of the superior curved line of the occipital bone, ligamentum nuchae, spinous processes of the seventh cervical and all the thoracic vertebrae and 138 MUSCLE TISSUE supraspinous ligaments; insertion, fibers converge to shoulder girdle; superior ones to outer third or half Muscles in the second layer of the back and on the dorsum of the shoulder. (Testut.) THE MUSCLES AND FASCIA OF THE TRUNK 139 of the posterior border of the clavicle (collar bone); middle fibers horizontally to inner margin of acromion and superior lip of spine of scapula; inferior fibers terminate in a triangular aponeurosis, which glides over a smooth surface at the inner extremity of the spine to be inserted into a tubercle at the outer portion of this surface. Latissimus Dorsi.^This is one of the largest and longest muscles in the body. Broad and flat at its origin, narrow at its insertion, it covers the lumbar region of the back and the lower half of the thoracic region. Origin, spinous processes of the lower six or seven thoracic vertebrae, posterior layer of lumbar aponeurosis which attaches it to the lumbar and sacral spines, and supraspinous ligament, from the outer lip of the iliac crest, also arises by three or four fleshy slips from three or four lower ribs. Its upper fibers pass horizontally outward, the middle obliquely upward, and the lower fibers vertically upward, they become narrowed into a tendon, IJ inches wide, which passes back of the arm-pit (axilla) in front of the teres major muscle, to be inserted into the bicipital groove on the anterior and upper aspect of the humerus (arm bone). Actions. — Depresses arm; draws it toward body (adducts); turns it inward; acts in striking a blow or chopping wood, etc.; when arms are firmly held in position, it assists the chest and abdominal muscles to suspend and draw forward or upward the whole trunk, as in climbing, etc. Nerve — subscapular from brachial plexus. The Muscles of the Thorax External intercostals. Triangularis sterni. Internal intercostals. Levatores costarum. Infracostales (subcostales) . Diaphragm. 140 MUSCLE TISSUE The Intercostal Muscles. — These are thin, flattened muscles extending between the margins of two adjacent ribs, fining the intervening spaces — called intercostal. These muscles are covered by the intercostal fascia, internally and externally, and a layer lies between the two muscles. The Subcostals. — ^The subcostals (infracostals) or muscles below the lower ribs consist of muscular and aponeurotic fibers, which are attached to the inner surface of one rib (usually lower ribs), and inserted into the inner surfaces of the first, second, or third rib below. They are placed on the parts of the ribs where the internal intercostal muscles end posteriorly. The Triangularis Stemi. — ^This is a thin, irregular- shaped muscle found on the posterior surface of the sternum (breast bone), and it passes to the costal cartilages of the ribs from the second to sixth inclusive. It is a single muscle. The Levatores Costarum (Elevators of the Ribs). — ^These are twelve in number found on each side of the verte- bral column external to the thoracic cavity. Origin, by small tendinous and fleshy bundles from the ex- tremities of the transverse processes of the seventh cervical and the eleven upper thoracic vertebrae; pass obliquely downward and outward to be inserted into the upper border, between the angle and tubercle of the rib, immediately below^ its vertebra of origin. Each of the lower elevator muscles divides into two slips, one of which is inserted as described above the other slip passes to the second rib below its origin; thus each of the lower ribs receives fibers from two vertebrae. Diaphragm. — ^This is a musculofibrous wall which divides the thoracic and abdominal cavities. It is dome-shaped; the convex, upper surface forms the floor of the thoracic cavity, and the concave lower surface the roof of the abdominal cavity. The attach- ments of the diaphragm are as follows : In front the THE MUSCLES AND FASCIJH OF THE TRUNK 141 lower six cartilages — internal surface, back of ensi- form; behind — from the lumbar vertebrae by two slips or crura; and from aponeurotic arches — the arcuate ligaments. The crura are found on the bodies of the lumbar vertebrae, on each side of the aorta. The internal arcuate ligament passes over the psoas muscle from the outer side of the body of the first lumbar vertebra to the lip of the transverse process. The Fig. 67 I'J'i ..\ iifjJiS Diaphragm, viewed from in front. (Testut.) external arcuate ligament passes over the quadratus lumborum from the second transverse process to the tip of the last rib. The fibers of the diaphragm arise from these ligaments. The muscular fibers on reaching the centre became fibrous, and form the central tendon of the diaphragm. The fibers are interwoven in every direction. The pericardium (the serous membrane covering the heart) is attached to the upper surface of this central tendon. 142 MUSCLE TISSUE There are three important openings in the dia- phragm, and several smaller ones. The esophageal opening transmits the esophagus and vagi nerves, the esophagus continues as the stomach below the dia- phragm; the aortic opening transmits the abdominal aorta, vena azygos major, and thoracic duct; it is the most posterior one; the opening for the inferior vena cava is the most anterior and transmits the large vein which carries the venous blood to the right side of the heart. The splanchnic nerves and the azygos minor veins pierce the diaphragm near the crura. The upper surface of the diaphragm is covered by peri- cardium in the centre, pleurae on the lateral surfaces, and the under surface is covered by peritoneum. Actions. — It is the chief muscle of respiration; thus when a deep breath is taken the diaphragm can be felt to extend downward making pressure on the abdominal organs, and at the same time increases the vertical diameter of the thoracic cavity, allowing the lungs to fill more readily with air. The diaphragm also contracts