The last I to 5 of these vertebrae have movable ribs which do not reach the sternum, and are called cervico-dorsals.
(I) Cervical vertebrae, or those between the skull and the first vertebra which is connected with the sternum by a pair of complete ribs.
The median and posterior extension of the body of the sternum is a direct outgrowth of the latter, therefore FIG.
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.
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.
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.
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.
Yet this distinguished zoologist selects the sternum as furnishing the key to his primary groups or " Orders " of the class, adopting, as Merrem had done long before, the same two divisions Cartnatae and Ratitae, naming, however, the former Tropidosternii and the latter Homalosternii.
Him from making known to the world the rest of his researches in regard to the other bones of the skeleton till he reached the head, and in the memoir cited he treats of the sternum of only a portion of his first " Order."
As it is, so much of them as we have are of considerable importance; for, in this unfortunately unfinished memoir, he describes in some detail the several differences which the sternum in a great many different groups of his Tropidosternii presents, and to some extent makes a methodical disposition of them accordingly.
Important as are the characters afforded by the sternum, that bone even with the whole sternal apparatus should obviously not be.
The skull and sternum were at the time unknown, and indeed the whole order, without doubt entirely extinct, rested exclusively on the celebrated fossil, then unique, Archaeopteryx.
2 The notion of the superiority of the palatal bones to all others for purposes of classification has pleased many persons, from the fact that these bones are not unfrequently retained in the dried skins of birds sent home by collectors in foreign countries, and are therefore available for study, while such bones as the sternum and pelvis are rarely preserved.
Pp. 403-408), to which were assigned as other characters vertebrae of a saddle-shape and not biconcave, a keelless sternum, and wings consisting only of the humerus.
Hesperornis too, with its keelless sternum, had aborted wings but strong legs and feet adapted for swimming, while Ichthyornis had a keeled sternum and powerful wings, but diminutive legs and feet.
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.
13 and 20), may in part represent in the adult the sternum of the excalated praegenital somite.
X, The sternum of the pectiniferous somite.
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.
(Original as preceding.) appendages on the sternum of the 3rd somite.
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.
No 1 Internally there Is a great difference in the form of the posterior margin of the sternum, as long ago remarked by Nitzsch.
2 It possesses only a single pair of posterior " emarginations on its sternum, in this respect resembling the Ruff.
- Characteristic features of the sternum are the following.
The anterior margin of the sternum, between the right and left anterior lateral processes receives in sockets the feet of the coracoids.
But the latter used this privilege wisely and well-not, after the manner of De Blainville and others subsequent to him, relying solely or even chiefly on the character afforded by the posterior portion of the sternum, but taking also into consideration those of the anterior, as well as of the in some cases still more important characters presented by the pre-sternal bones, such as the furcula, coracoids and scapulae.