(I) Cervical vertebrae, or those between the skull and the first vertebra which is connected with the sternum by a pair of complete ribs.
(Original as preceding.) appendages on the sternum of the 3rd somite.
The last I to 5 of these vertebrae have movable ribs which do not reach the sternum, and are called cervico-dorsals.
The median and posterior extension of the body of the sternum is a direct outgrowth of the latter, therefore FIG.
The anterior margin of the sternum, between the right and left anterior lateral processes receives in sockets the feet of the coracoids.
The keel, or carina sterni, is formed as a direct cartilaginous outgrowth of the body of the sternum, ossifying from a special centre.
Often it reaches the keel of the sternum, with subsequent syndesmosis or even synostosis, e.g.
- Sternum of a Chick (Gallus domesticus) three days old, lower view, X three diameters.
Lindsay, " On' the Avian Sternum," P.Z.S., 1885; E.
Soc., 1875; " Monograph on the Structure and Development of the Shoulder-girdle and Sternum," Ray Soc. London, 1868; W.
The chief muscular mass, arising from the sternum in the shape of a U, is the pectoralis muscle; its fibres converge into a strong tendon, which is inserted upon the greater tubercle and upper crest of the humerus, which it depresses and slightly rotates forwards during the downstroke.
This arises mostly from the angle formed by the keel with the body of the sternum, passes by a strong tendon through the foramen triosseum, and is inserted upon the upper tubercle of the humeral crest, which it rotates and abducts.
The extent of the origin of this muscle from the sternum, on which it leaves converging, parallel or diverging impressions, is of some taxonomic value.
The whole ventral surface of the pericardium is exposed when the sternum is removed.
The keel is pushed back to the distal third of the sternum, whilst the original anterior margin of the keel is correspondingly elongated,and the furcula fused with the rostral portion.
Nidifugous; vomer large; sternum without processus obliqui.
The ventral region of the thoracic skeleton is complex, each segment usually possessing a median sternum with paired episterna (in front) and epimera (behind).
I, Fore-leg and pro-sternum (S) ta, Tarsal segments.
The ejaculatory duct which opens on the ninth abdominal sternum in the adult male arises in the tenth abdominal embryonic segment and subsequently moves forward.
In the following year .another set of hints - of a kind so different that probably no one then living would have thought it possible that they should ever be brought in correlation with those of Nitzsch - are contained in a memoir on Fishes contributed to the tenth volume of the Annales du Museum d'histoire naturelle of Paris by Etienne Geoffroy St-Hilaire in 1807.1 Here we have it stated as a general truth (p. too) that young birds have the ' sternum formed of five separate pieces - one in the middle, being its keel, and two " annexes " on each side to which the ribs are .articulated - all, however, finally uniting to form the single " breast-bone."
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.
The most novel feature, and one the importance of which most ornithologists of the present day are fully prepared to admit, is the separation of the class A y es into two great divisions, which from one of the most obvious distinctions they present were called by its author Carinatae' and Ratitae, 2 according as the sternum possesses a keel (crista in the phraseology of many anatomists) or not.
6 There is no appearance of his having at all taken into consideration the far more trustworthy characters furnished by the anterior part of the sternum, as well as by the coracoids and the furcula.
So far as his introductory chapter went - the development of the sternum - he was, for his time, right enough and somewhat instructive.
At the very beginning of the year 1832 Cuvier laid before the Academy of Sciences of Paris a memoir on the progress of ossifi cation in the sternum of birds, of which memoir an cuvier abstract will be found in the Annales des sciences and naturelles (xxv.
Detail, illustrating his statements by the preparations he exhibited, the progress of ossification in the sternum of the fowl and of the duck, pointing out how it differed in each, and giving his interpretation of the differences.
But it was now made to appear that the struthious birds in this respect resembled, not only the duck, but a great many other groups - waders, birds-of-prey, pigeons, passerines and perhaps all birds not gallinaceous - so that, according to Cuvier's view, the five points of ossification observed in the Gallinae, instead of exhibiting the normal process, exhibited one quite exceptional, and that in all other birds, so far as he had been enabled to investigate the matter, ossification of the sternum began at two points only, situated near the anterior upper margin of the side of the sternum, and gradually crept towards the keel, into which it presently extended; and, though he allowed the appearance of detached portions of calcareous matter at the base of the still cartilaginous keel in ducks at a certain age, he seemed to consider this an individual peculiarity.
The duck, on the other hand, when newly hatched, and for nearly a month after, has the sternum wholly cartilaginous.
Then, it is true, two lateral points of ossification appear at the margin, but subsequently the remaining three are developed, and when once formed they grow with much greater rapidity than in the fowl, so that by the time the young duck is quite independent of its parents, and can shift for itself, the whole sternum is completely bony.
In their case the sternum begins to ossify from three very distinct points - one of which is the centre of ossification of Nitzsch's grouping.
L'Herminier arrived at the conclusion that, so far from there being only two or three different modes by which the process of ossification in the sternum is carried out, the number of different modes is very considerable - almost each natural group of birds having its own.
2 It possesses only a single pair of posterior " emarginations on its sternum, in this respect resembling the Ruff.
No 1 Internally there Is a great difference in the form of the posterior margin of the sternum, as long ago remarked by Nitzsch.
1, The sternum of the first opisthosomatic or genital somite covering the V "' genital aperture and the first pair of lung sacs.
Intromittent organ of male beneath sternum of the 1st somite of the opisthosoma.
Respiratory organs tracheal, opening by a pair of stigmata situated immediately behind the basal segments of the 6th pair of appendages on what is probably the sternum of the 2nd opisthosomatic somite and also in some cases upon the 5th segment of the legs.
The meeting of the coxae of all the prosomatic limbs in front of the pentagonal sternum; the space for a genital operculum; the pair of pectens, and the absence of any evidence of pulmonary stigmata are noticeable in this specimen.
13 and 20), may in part represent in the adult the sternum of the excalated praegenital somite.
X, The sternum of the pectiniferous somite.
A diagnosis covering all the Ratitae (struthio, rhea, casuarius, dromaeus, apteryx and the allied fossils dinornis and aepyornis) would be as follows - (i) terrestrial birds without keel to the sternum, absolutely flightless; (ii) quadrate bone with a single proximal articulating knob; (iii) coracoid and scapula fused together and forming an open angle; (iv) normally without a pygostyle; (v) with an incisura ischiadica; (vi) rhamphotheca compound; (vii) without apteria or bare spaces in the plumage; (viii) with a complete copulatory organ, moved by skeletal muscles.
Be that as it may, he declares that characters drawn from the sternum or the pelvis - hitherto deemed to be, next to the bones of the head, the most important portions of the bird's framework - are scarcely worth more, from a classificatory point of view, than characters drawn from the bill or the legs; while pterylological considerations, together with many others to which some systematists had attached more or less importance, can only assist, and apparently must never be taken to control, the force of evidence furnished by this bone of all bones - the anterior palatal.
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.