OSTEOLOGY— THE DESCRIPTION OF BONES (Part 2)

with the palate bone, also a part of the floor of the orbit. It contains the hollow space just above the canine tooth, called the antrum of Highmore. The latter communicates with the nasal chamber and is frequently the seat of inflammation. This bone articulates with its fellow of the opposite side, the nasal, lacrymal, frontal, ethmoid, palate, malar, vomer, inferior tur- binate, and sometimes the sphenoid. The Palate Bones. — They are two in number situated at the back part of the nasal fossse; they are lodged between the maxilla and the pterygoid processes of the sphenoid. Each bone assists in the formation of the floor and outer wall of the nasal cavity, roof of the mouth, and floor of the orbit. The Turbinated Bones. — They are situated one on each side of the outer wall of the nasal fossse. Each consists of a layer of thin, spongy bone, curled upon itself like a scroll — hence its name, turbinated The Malar Bone. — This bone is quadrangular, and is situated at the upper and outer part of the face. It forms the prominence of the cheek, part of the outer wall and floor of the orbit, and part of the temporal and zygomatic fossse. It articulates with the frontal, sphenoid, temporal, and the maxilla. The Mandible or Lower Jaw. — This is the largest and strongest bone of the face. It consists of a horizontal portion called the body, which forms the chin, and two perpendicular rami, which join the body to form the angle of the jaw. It articulates by its condyles with the glenoid cavity of the tympanic portion of the temporal bone. The horizontal portion serves for the lodgement of the lower teeth. The Hyoid Bone. — ^This is a bony arch, shaped like a horseshoe, and consisting of five segments — a body, two great cornua, and two lesser cornua. It is situated in the neck in the receding angle below the chin. It is BONES OF THE HEAD 69 supported by the stylohyoid ligaments attached to the lesser cornua of each side.. The attachment of muscles help to hold this bone in position and acts as a fixed point for the muscles of swallowing and articulating. Below it is attached to the larynx by the thyrohyoid membrane. The hyoid bone can be felt just above the Adam's apple (pomum Adami). It also affords attachment to the muscles which lower the jaw, depress the tongue, and aid as accessory muscles of respiration. Fig. 32 Orbital surface Infraorbital groove Union wit/i lacrimal bone Inferiorten/poral ^ surface ^ r^ ~ ^, _ Post, dental canals Maxillan/ tuberosity -"-"^ ""^V-^ Zygomatic process ' Frontal process , .Zammal ?nar^in Infraorbital margin ^ Anterior surface 'Infraorbital forajnen ^,.' Canine fossa ' ' '^Palatine process . . . -Ant. nasal spine Aloeolar process Right upper jaw bone, maxilla, fi:om without. The Skull as a Whole. — At birth the skull is large in comparison with the other parts of the skeleton. The face is small and equals only about one-eighth of the bulk of the cranium, as compared to the size of the face in the adult which equals about one-half of the size of the skull. Ossification of the bones of the skull in the infant is not complete; they are held together by membranous tissue and these intervals between the bones are termed fontanelles. There are six: Two, 70 OSTEOLOGY anterior and posterior, and four, an anterolateral and posterolateral on either side. Fig. 33 Skull at birth, showing the anterior and posterior fontanelles. (Gray.) Fig. 34 The lateral fontanelles. (Gray.) The anterior fontanelle is the largest and is situated at the junction of the sagittal, coronal, and inter- frontal sutures; it is lozenge-shaped and measures PLATE I Anterior Aspect of the Skull. PLATE 11 kv. t-' v^ Lateral Aspect of the Skull. BONES OF THE HEAD 71 about 1^ inches from before backward and 1 inch from side to side. Pulsation can be felt over this fontanelle up until the twelfth to twenty-fourth month. It usually disappears by ossification after the second year, but cases have been reported when it persists throughout life. The posterior fontanelle is triangular in form and is situated at the junction of the superior angles of the parietal bones with the occipital bone. The lateral fontanelles are irregular in shape, and are located at the antero-inferior and postero-inferior angles of the parietal bones respectively. The posterior and lateral fontanelles close shortly after birth. The lack of ossification in the bones of the skull favors the over- lapping of the bones or moulding of the infant's head during parturition, thus facilitating delivery and pre- venting injury to the mother and child; of course, barring some abnormal condition at the time of birth. In adults the skull bones are closely fitted by uneven edges, there being interposed a little fibrous tissue continuous with the periosteum, the dentations are confined to the external table, the edges of the inner table lying in apposition. The lower jaw has a mov- able articulation differing from the others. The bones forming the vertex or superior surfaces of the skull are: frontal, two parietal, two temporal (squamous and mastoid portions), and great wing of the sphenoid. The Orbital Fossae or Orbits. — These are pyramidal in shape, with their bases turned forward and outward. They are just below the supraorbital arches; their inner walls are nearly parallel and the outer walls diverge at slight right angles to each other. Each is formed by seven bones or eleven for the two orbits — the frontal, sphenoid, ethmoid, lacrymal, palate, malar, maxilla. The roof of each is formed by the orbital plate of the frontal and small wing of the sphenoid; the floor, by the malar, maxilla, and orbital 72 OSTEOLOGY plate of the palate; inner wall, by the nasal process of the maxilla, lacrymal, ethmoid, and body of the sphenoid; outer wall, by the malar and frontal and great wing of the sphenoid. The Nasal Fossa or Cavities. — ^These are placed one on each side of a median vertical wall. They open in front by the anterior nasal apertm-e (nares) and behind by the posterior nares. They cominunicate with the sinuses (air spaces) of the frontal, sphenoid, and antrum of Highmore, the latter is in the body of the maxilla, and the ethmoidal cells. Thus the danger from infec- tion entering these air spaces following an abscess for- mation, influenza, etc., may readily be understood. THE VERTEBRAL COLUMN AS A WHOLE The vertebral or spinal column is a central axis upon which other parts are arranged, situated in the median line at the posterior part of the trunk; above it sup- ports the head, by having the first vertebra receive the condyles of the occipital bone; laterally, the ribs, and it rests on the sacrum. It is made up of thirty- three separate vertebrae, imposed one upon the other with an intervertebral layers of cartilages between each one, and held in firm relationship by means of ligaments. The vertebrae are divisible into seven cervical, twelve thoracic, five lumbar, five sacral, and four coccygeal. The cervical, thoracic, and lumbar verte- brae remain separate throughout life, and are known as true or movable vertebrae; but the sacral and coccy- geal vertebrae are firmly united in the adult, so as to form two bones — five entering into the formation of the sacrum and four into the terminal bone of the spine or the coccyx. The sacral and coccygeal verte- brae are called the immovable vertebrae. The average length of the vertebral column is about Fig. 35 1st cervical or Atlas. Coccyx. Lateral view of the vertebral column. (Gray.) 74 OSTEOLOGY twenty-six to twenty-seven inches measured along the curved anterior surface of the column. The cervical part measures about five, the thoracic about eleven or twelve, the lumbar about seven inches, and the sacrum and coccyx the remainder. Viewed from the side it presents several curves. The cervical curve commences at the odontoid process of the second vertebra, and ends at the middle of the second thoracic ; it is convex in front, but not as marked as the other curves. The thoracic curve is concave forward, commences at the middle of the second thor- acic, and ends at the middle of the twelfth thoracic. The lumbar curve, commences at the middle of the twelfth thoracic and ends at the sacrovertebral angle (about the junction of the sacrum with the fifth lum- bar vertebra). It is convex in front; the convexity being more marked in the lower three lumbar verte- brae. These curves and convexities are formed by the bodies of the vertebrae. While the posterior aspect is formed by the extending spinous processes which usually can be felt underneath the skin and fascia, no matter how stout the individual. Laterally the column presents the transverse processes. The spinal cord, membranes, origin of spinal nerves, and blood-supply are within the spinal canal — formed by the inter- vertebral fibrocartilage, body, and arched lamina of the vertebrae; the latter fusing posteriorly, complete its boundaries. Posteriorly, the spinous processes occupy the median line, in a depression known as the vertebral groove running along the middle of the back. In the cervical region the processes are short and bifid, sloping backward and a little downward. The seventh cervical is the most prominent and can always be seen and felt beneath the skin, therefore its name — vertebra prominens. The thoracic processes are oblique above, more oblique in the middle, and below are nearly horizontal; in the lumbar region they are horizontal. The transverse processes of the atlas are THE VERTEBRAL COLUMN AS A WHOLE 75 long; of the axis, short; then extending in size until the first thoracic is reached, thence diminishing to the last dorsal, and becoming suddenly much longer in the lumbar region. The intervertebral foramina are always in front of the articular processes excepting those of the atlas and the upper ones of the axis. They are named from the upper of the two vertebrae which go to form them, excepting in the cervical region, where there are eight, the fissure between the skull and atlas being called the first. The spinal canal is narrowest in those por- tions having the least motion, viz., the dorsal and sacral regions. It is round and f of an inch in diameter in the dorsal region; it is triangular, with the apex behind, in the cervical and lumbar regions; and largest of all in the cervical region. The cervical vertebrae each have a foramen (costotransverse) in their two transverse processes for the vertebral artery. Fig. 36 Anterior tubercle of trans- verse process. Foramen for vertebral artery. Posterior tubercle of transverse process. Transverse process. Superior articular process. Inferior articular process. A cervical vertebra. (Gray.) General Characteristics of a Vertebra. — A typical vertebra is made up of two parts, an anterior solid 76 OSTEOLOGY portion, and a posterior portion, the arch or neural canal. The arch is formed by two pedicles, and two laminae, supporting seven processes — viz., four articular, two transverse, and one spinous. Taking a typical vertebra — the tenth thoracic, for example. The body is cylindric; the upper and lower surfaces are flat, with a rim around the circumference. The front Fig. 37 Superior articular process. Demi-facet for head of rib. Facet for tubercle of rib. Demi-facet for head of rib. Inferior articular process. A dorsal vertebra. (Gray.) and sides are convex from side to side and concave from above downward. The back is slightly concave from side to side. The neural arch is completed laterally by two processes of bone arising from the postero-external aspect of the body, called pedicles, and the latter continue — as lamina — behind, where they meet to complete the posterior aspect of the neural arch. The upper and lower borders of the pedicles THE VERTEBRAL COLUMN AS A WHOLE 77 form intervertebral notches, which complete, with the neighboring pedicle of the vertebra, intervertebral foramina. The spinous process projects backward from the junction of the two laminae. The transverse processes, one on either side, project outward from the arch at the junction of the pedicle with the lamina. The articular processes, two superior and two inferior, extend upward and downward respectively at the point of origin of the transverse processes. Fig. 38 Tubercle Biugrahi of nedion of odontoid, process. Diagram of section of liyaincid. Foramen for vertebral artery. Groove for vertebral artery and 1st cervical nerie. Rudimentary spinous process.. First cervical vertebra or atlas. (Gray.) The Atlas (First Cervical Vertebra). — ^This, sometimes called rotation vertebra, has no body or spinous process, but is a large ring with articular and transverse processes. The posterior part of the ring or arch corresponds to the neural canal of the other vertebrse; the anterior part is occupied by the odontoid process of the axis (second cervical vertebra). This first vertebra and its relation with the odontoid process of the axis, below, and its superior articular surface receiving the condyles of the occipital bone, held in position by ligaments, permits the head to rotate and bend forward and backward, as in turning the head from side to side, and in nodding. The odontoid process of the axis is held in position by a transverse 78 OSTEOLOGY ligament passing posterior to it and attached to the tubercle on the the inner surface of the lateral mass on either side of the arch, and by check ligaments extending from the apex of the odontoid process to the occipital bone. The atlas has a foramen (the costo- transverse) for the vertebral artery in its transverse process. Fig. 39 Odontoid process. Rough surface for check ligaments. Artiadar surface for tramverse ligament. Spinous process.- Articiilnr surface foi atlas. Body. \ Transverse p) ocess. Inferior articular process. Second cervical vertebra or axis. (Gray.) The Axis (Second Vertebra). — This possesses a strong, prominent process, tooth-like in form, which arises perpendicularly from the upper surface of the body. The body in front overlaps the vertebra below. The tip of the odontoid process affords attachment to the check ligaments (see Fig. 52, page 109) and has an articular surface anteriorly, which articulates w^ith the atlas, and an articular facet behind for the transverse ligament, which holds it firmly in position. The pedi- cles and laminae form the neural arch in the same manner as the atlas and other vertebrae. The spinous process is larger than the one of the atlas. The trans- verse processes are small, and are perforated by the foramen for the vertebral artery. THE THORAX AS A WHOLE 79 The Sacram and Cocc3rx. — ^The sacrum and coccyx are the result of the fusing of the lower nine vertebrae into two bones, five to form the sacrum and four the coccyx. The sacram is much larger than the coccyx, is located between the two iliac bones, articulating above with the fifth lumbar vertebra, below with the coccyx, and is perforated with foramina which transmit the spinal nerves. The coccyx is pyramidal. Its vertebrae are very rudimentary, and it possesses a trace of the neural arch and transverse processes of the typical vertebra. THE THORAX AS A WHOLE The thorax is an osseocartilaginous cage, conical and flattened from before backward. The short antero- posterior diameter is characteristic of man, but in the lower mammals and human fetus it is longer than the transverse diameter. The posterior surface is convex forward, formed by the twelve thoracic vertebrae and back part of ribs; on either side the sulcus pulmonalis is formed by the ribs as they project backward, so that the weight of the body is more equally distrib- uted around the vertebral column. The anterior surface is flattened and slightly convex, is formed by the sternum and costal cartilages, and lies at an angle of 20 or 25 degrees with the posterior. A horizontal anteroposterior diameter taken from the base of the ensiform is 8 inches (20 cm.); the transverse at the eighth or ninth ribs is 11 inches (28 cm.); the vertical anteriorly is 6 inches (15.5 cm.); and posteriorly is 12 inches (31.5 cm.). The lateral surfaces are convex; formed by the ribs, separated from each other by the spaces (intercostal). The superior or upper opening of the thorax, the inlet, is reniform in shape, being broader from side to side 80 OSTEOLOGY than before backward. It is bounded behind by the first thoracic vertebra; in front, by the upper border of the sternum, and on either side by the first rib. Fig. 40 *^— First thoracic The thorax. Ventral view. (Gray.) It slopes downward and forward so that the anterfor boundary is on a lower level than the posterior. The anteroposterior diameter is about 2 inches (5 cm.). THE THORAX AS A WHOLE 81 and the, transverse about 4 inches (10 cm.)- The parts which pass through the upper opening are, from before backward in or near the middle line — the sternohyoid and sternothyroid muscles, the remains of the thymus gland, the trachea (windpipe), the esophagus (gullet), thoracic duct, inferior thyroid veins, longus colli muscle of each side, bloodvessels and nerves. The inferior or lower opening is formed by the twelfth thoracic vertebra behind, by the twelfth ribs at the sides, and in front by the eleventh, tenth, ninth, eighth, and seventh costal cartilages, which ascend on either side to form the subcostal angle, from the apex of which the ensiform cartilage projects. The lower opening is wider transversely than from before backward. It slopes obliquely downward and back- ward, so that the cavity of the thorax is much deeper behind than in front. The diaphragm closes in the opening forming the floor of the thorax, and has passing through it the inferior vena cava, the esophagus, and vagi nerves, the aorta, thoracic duct, vena azygos major, and sometimes splanchnic nerves. The thorax contains the lungs and their pleurae, the heart and its