Sternum

“ Arising from the sternum, as we have above indicated, this portion is directed outwards, to be joined with the terminal aponeurosis of the sterno-humeral, and with that which covers the internal surface of the forearm.
All things considered, the sterno-humeral muscle may be regarded as the representative of the upper fibres of the great pectoral of man, of which the attachments, owing to the more or less complete absence of the clavicle in the domestic mammals, the fibres must be concentrated on the [132] sternum ”

“ During the act of inspiration the sternum is depressed, the angle between the vertebral and the sternal ribs is made less acute, and the thoracic cavity proportionately enlarged; the air then rushes into the lungs and into the thoracic receptacles, while those of the abdomen become flaccid. When the sternum is raised, or approximated toward the spine, part of the air is expelled from the lungs and the thoracic air-sac through the trachea, and part is driven into the abdominal receptacles, which are thus alternately enlarged and diminished with the expansion and the contraction of the thorax. ”

“ The removal of the sternum gives a loss of resistance to the manipulations upon the back of the cadaver, and the turning-over of the body after it has been opened anteriorly is usually an unpleasant procedure because of the dripping of blood and other fluids. When it is found necessary to examine the cord posteriorly after the opening of thorax and abdomen it is better to fill these cavities with tow or excelsior, replace the sternum and sew up the anterior skin-incision before turning the body over. ”

“ This structure is found in all the Amniota except the Ophidia, Chelonia, and some of the Amphisbænæ.
From the older researches of Rathke, and from the newer ones of Götte, etc., it appears that the sternum is always formed from the fusion of the ventral extremities of a certain number of ribs. The extremities of the ribs unite with each other from [Pg 563] before backwards, and thus give rise to two cartilaginous bands. These bands become segmented off from the ribs with which they are at first continuous, and subsequently fuse in the median ventral line to form an unpaired sternum. ”

“ The sterno-prescapular muscle, being covered by the sterno-humeral, has little interest for us. It arises from [134] the sternum, and is directed towards the angle formed by the junction of the scapula and humerus; then it is reflected upwards and backwards, to terminate on the anterior margin of the shoulder by insertion into the aponeurosis, which covers the supraspinatus muscle. ”

“ Moreover, the author goes on to remark that in adult birds trace of the origin of the sternum from five centres of ossification is always more or less indicated by sutures, and that, though these sutures had been generally regarded as ridges for the attachment of the sternal muscles, they indeed mark the extreme points of the five primary bony pieces of the sternum. ”

“ In certain edentates, notably [75] the anteaters and the extinct †ground-sloths, these sternal ribs, at their lower ends, are provided with head and tubercle, for articulation with the sternum.
The sternum, or breast-bone, is made up of a number of distinct segments, usually broad and flat, but often cylindrical, which may unite, but far more commonly remain separate throughout life. The number, size and form of these segments often give useful characters in classification. The first segment, or manubrium, has quite a different shape from the succeeding ones and is considerably longer. ”

“ Those who have not directed their attention to the subject are hardly aware what a little distance there is between the cricoid cartilage and the upper part of the sternum. In a person of the average height sitting with [Pg 16] the neck in an easy position, the distance is barely one inch and a half. When the neck is well stretched, about three-quarters of an inch more is gained. Thus, we have (generally) not more than seven or eight rings of the trachea above the sternum. None of these rings can be felt externally. The second, third, and fourth are covered by the isthmus of the thyroid gland. ”

“ In well-formed people, the sternum is a little convex, externally, and concave, internally, permitting all possible room for the thoracic viscera. In Seurat, however, this order of things is changed, the outer surface of the breast-bone being concave, and the internal convex. ”

“ The sternum is utterly unlike that of any other species, the anterior portion of the keel being aborted, and the posterior correlated with a flattened area of thick naked skin, on which the bird mainly rests. These modifications are no doubt connected with the extraordinarily large crop, which is supported by the furcula and the fore-part of the breast-bone, being received in a cavity of the pectoral muscles; the whole organ is decidedly muscular, and contains two divisions with a partial constriction between them. ”

“ The course of the arteria innominata corresponds with a line drawn from the middle of the junction of the first with the second bone of the sternum, to the right sterno-clavicular joint. When the artery rises higher than usual into the neck, its pulsation can be felt in the fossa above the sternum. ”

“ The fact that he has lain down may be taken as an indication that improvement has taken place. The peculiarity is due to the sharp outline of the horse’s sternum inferiorly so that in lying down he is compelled to rest on his side and the whole weight of the body tends to compress the chest. In the ox, sheep, pig and dog, which can rest on the sternum, breathing can be carried on with comparative ease in the recumbent position, and these animals accordingly do not necessarily stand except in very extensive and violent affections of the chest. ”

“ Ligature of Right Subclavian.—First Part.—Operation.—An incision just at upper edge of sternum and right clavicle, extending from inner edge of left sterno-mastoid transversely to outer border of right sterno-mastoid through skin, platysma, and exposing sterno-mastoid, to be joined at an angle by a second incision, which, two, three, or even four inches long, must extend along inner border of right sterno-mastoid. Flap to be raised upwards and outwards. ”

“ This sternum develops a bird-like keel. Both Mole and Bat are regarded as differing from Pterodactyles in the bone giving attachment to the clavicles instead of to the coracoids. The proximal part of the sternum in both the living animals, gives attachment to but one pair of sternal « 31 » ribs. The Pterodactyle sternum otherwise differs from the Bats in having the articulations for the coracoids close together, of a peculiar concavo-convex character, with a massive portion or keel prolonged forward in front of the coracoid articulations. ”

“ SHOULDER-GIRDLE AND FORE LIMB STERNUM
The sternum is always a distinguishing part of the bony structure of the breast. In Crocodiles it is a cartilage to which the sternal ribs unite; and upon its front portion a flat knife-like bone called the interclavicle is placed. In lizards like the Chameleon, it is a lozenge-shaped structure of thin bony texture, also bearing a long interclavicle, which supports the clavicular bones, named collar bones in man, which extend outward to the shoulder blades. ”

“ It is very doubtful if the Anura possess a true sternum, if by sternum we understand a medio-ventral apparatus which owes its origin to the ventral portions of ribs. The so-called sternal apparatus of the Anura consists of two pieces. One, anterior, variously named episternum, presternum, or omosternum, rests upon the united precoracoids and extends headwards, being either styliform or broadened out. Sometimes it is partly ossified, with a distinct suture at its base; this is the case especially in the Firmisternia ”

“ At the same time he states that authors who have occupied themselves with the sternum alone have often produced uncertain results, especially when they have neglected its anterior for its posterior part; for in truth every bone of the skeleton ought to be studied in all its details. ”

“ If a prominent breast is admired and selected by fanciers, the sternum might shorten in assuming a more forward and vertical position. If the shortening of the sternum is entirely due to disuse, it seems strange that Darwin has not noticed any similar shortening in the sternum of the duck. But selection has not tended to make the duck elegant, or "pigeon-breasted" ”

“ More serious congenital malpositions, but of less practical importance, are the cases of ectopia cordis, which may exist in all grades, from simple failure of closure in the sternum—fissura sterni—to the most extreme condition, in which the naked heart lies outside the chest-wall. ”

“ Spaces and clefts within the cartilage may be filled with new-formed bone-marrow.
9. Sternum. Note shape (pigeon-breast, “shoemaker’s,” rounded, scaphoid, bifid, anomalies of ensiform, etc.) , fractures (in marked osteoporosis the bones may break during removal) , erosions (aneurisms, tumors) , tuberculous and syphilitic caries, gummata, perforations, etc. Under surface of sternum should be smooth, shining, translucent and grayish. In chloroma the under surface may present a uniform greenish layer 1⁄2-1 cm. thick. Bone-marrow of sternum is normally red and lymphoid in character ”

“ The principal theory which he hence conceived himself justified in propounding was that instead of five being (as had been stated) the maximum number of centres of ossification in the sternum, there are no fewer than nine entering into the composition of the perfect sternum of birds in general, though in every species some of these nine are wanting, whatever be the condition of development at the time of examination. ”

“ The rami of the mandible are nearly straight and become united in a long symphysis. Some of the ribs have well developed capitula articulating with the vertebral centra. The sternum is almost always composed of several pieces as in other mammals, and several pairs of ribs are connected with it. There are always five digits to the manus, though the first and fifth are usually very little developed. ”

“ The vertebrae are generally without epiphyses to their centra. The cervical vertebrae in living forms have saddle-shaped articulating surfaces, and many of them bear ribs. The thoracic ribs in almost all birds have large uncinate processes. The sternum is very large, and the ribs are always attached to its sides, not as in many reptiles [296] to any backwardly-projecting process or processes. The sternum ossifies from two or more centres.
The skull is extremely light, and its component bones show a great tendency to fuse together completely. ”

“ Antennæ of three main segments which lie when at rest in a groove. Three thoracic segments, always free, each consisting of a notum and a sternum. The sterna of the second and third segments are further divided into a sternum, an episternum and an epimeron, the two latter constituting the pleura. Wings and rudiments of wings entirely absent. [109] Abdomen of ten segments of which the sternite of the first segment is suppressed. Abdomen enormously swollen in pregnant females of certain species. Combs frequently present on head, thorax, and abdomen. Legs developed for leaping. Coxa powerful ”

“ In malformation the heart's action and the pulse are rapid, and a murmur can often be heard. The thoracic outline may deviate from the usual antero-posterior flattening by the sternum being prominent in cases where the heart, instead of its usual position to the left, is placed more centrally, as comes in certain defects of development. ”

“ One other change may be noted in some frozen sections, and is occasionally observed in examination of the chest— namely, a more marked inward curve in the lower part of the sternum than is usually found in men, whereby the antero-posterior diameter of the lower part of the chest is somewhat diminished. ”

“ The sternomastoid, is a large, thick muscle, which passes obliquely across the side of the neck, being inclosed between two layers of deep fascia. It has its origin at the sternum and clavicle and attaches to the mastoid process of the temporal bone. By making the perpendicular incision in the lower third, in as much as the muscle slightly covers the artery, it can either be cut or pushed to the outside of the incision. It is best to push the muscle to the outside with the thumb, and with the handle of the scalpel, work down deep through the areolar tissue. ”

“ Intolerable heat at the chest, at two o’clock, violent pain and burning sensation at the sternum.
Sixth day.—360. Restless sleep. Nervousness, impatience, at half past 12. Dry heat in the hands.
Seventh day.—Small vesicular pimple at the right wrist-joint. Marked feeling of heaviness from the parietal bone to the lower attachment of the sterno-mastoideus muscle, at the upper side of the sternum. 365. At two o’clock: the [79] weight, at times, descends to the forehead, with heat. Small pimple on the right wrist, red at its base, containing a fluid. ”

“ Prosternal spine: the curved mucro in Elateridae which extends backward into a meso-sternal cavity: the cone or tubercle between fore-legs in some Orthoptera.
Prosternal suture: that suture of pro-thorax which separates the sternum front the pleural pieces.
Prosternellum: the sternellum of the prothorax
Prosternum: the fore-breast: the sclerite between the fore-legs.
Prostheca: a mandibular sclerite set with hair, articulated to the basalis - q.v. -and equal to the lacinia of the maxilla. ”