Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25759/295/
AVES. 
283 
( Upupu)j the sternum again becomes dimi¬ 
nished in size, and presents the two fissures on 
the posterior margin ; the keel is moderately 
developed ; the manubrial process is produced 
anteriorly; it is of a compressed form in the 
Hoopoe, but thick, and bifurcate in the 
Creepers; there are no costal processes. 
In the Wood-peckers the keel of the ster¬ 
num is more feebly developed, its inferior 
margin is straight, and the angle formed by its 
union with the anterior margin truncate. The 
manubrial process enlarges as it advances 
forwards, and is bifurcate at the extremity. 
The costal processes are also long, and curved 
forwards; the posterior margin has four deep 
notches (ff,ßg. 129). 
In the Trogons, Kollers (Coracias), King¬ 
fishers, Bee-eaters ( Merops), Toucans, and 
Touracos, the sternum is characterized by two 
fissures on either side at the posterior margin. 
In the Parrot tribe the sternum again singu¬ 
larly resembles in its integrity that of the higher 
Raptures,being in somespecies simply perforated 
on either side near the posterior margin, and in 
others wholly ossified. It is, however, narrower 
in proportion to its breadth. The keel is well 
developed, its inferior margin concave, its an¬ 
terior one describing a sigmoid flexure ; their 
angle of union rounded. The costal depres¬ 
sions occupy almost the entire lateral margins 
of the sternum. The manubrial process is 
slightly developed, trihedral, and truncate at 
the extremity. 
In the Pigeons, which unite the In- 
sessorial to the Gallinaceous order, the ster¬ 
num is narrow, but the keel is deep, with its 
inferior border convex, and the anterior one 
curved forwards, thin and trenchant ; the ma¬ 
nubrial process is strong and bifurcated; the 
costal processes short. The posterior margin 
is cleft by two fissures on either side of the 
mesial plane, the lateral and superior fissures 
being the deepest; the mesial ones are occasion¬ 
ally converted into a foramen. The costal surface 
of the lateral margin is, as in the Gallinaceous 
birds, of very little extent. In the Crown 
Pigeon the superior fissures are so deep and 
wide as to convert the rest of the lateral margin 
into a mere flattened process, which is dilated 
at the extremity. 
In the true Rasores the four posterior fis¬ 
sures of the sternum are so deep and wide 
from its defective ossification, as to give to the 
lateral parts of this bone, or hypo-sternal 
elements, the appearance of a bifurcated pro¬ 
cess extending backwards from the costal 
margin. The mesial fissures are here the 
deepest, extending as far as the anterior 
border of the keel. This part is short, straight, 
or very slightly convex inferiorly; concave at 
the anterior margin, which is formed by two 
ndges which converge to it from the anterior 
margin of the sternum. This margin is con¬ 
vex laterally, and largely excavated for the 
coracoid bones ; the depressions are continuous 
with each other, and the compressed manubrial 
process, arching over the canal, converts it into 
a foramen. The costal processes are prolonged 
upwards and forwards; the posterior lateral 
prooesses pass backwards exterior to die ribs, 
supporting them in the Capercailzie, like a 
semi-hoop ; these processes are dilated at their 
extremities. 
In the Grallatores or Waders the sternum 
corresponds in size to the shortness of the 
thoracic-abdominal cavity. In the ArdeicUe 
the grooves of the anterior surface pass reci¬ 
procally beyond the middle line, increasing the 
surface of attachment for the expanded lower 
and posterior extremities of the coracoid bone. 
In most of the genera the posterior margin pre¬ 
sents a single fissure on either side ; these in 
the Storks and Herons are wider at the com¬ 
mencement than at the termination. In the Plo¬ 
vers, Woodcocks, Avosets, and Oyster-catchers, 
it occupies the whole breadth of the sternum. 
In the Curlews, Ibises, and Spoonbills, there 
are two fissures on either side. In the Coots 
and Water-hens the single fissures on either 
side of the keel are long and narrow, and the 
lateral portions of the sternum extend back¬ 
wards beyond the middle, and become larger 
towards their extremities. 
Among the Natatores, file Albatrosses, 
Petrels, Pelicans, and Cormorants present a 
strong wide convex sternum, similar to the 
Storks and Herons; the keel is moderately 
developed, but prolonged anteriorly ; the pos¬ 
terior margin presents a single slight fissure 
on either side. In the Penguins, these fissures 
are of considerable extent (f,f,fig- 130,) ; but 
the keel of the sternum is well developed, 
even in the Aptenodytes ; its inferior border is 
straight. In the Gulls and Sea-swallows the 
sternum is of large size, wide, and convex ; 
it presents posteriorly two small and shallow 
fissures on either side, of which the lateral and 
superior are sometimes converted into foramina. 
The keel extends along the whole of the ster¬ 
num, but is of moderate depth, and convex 
inferiorly. 
In the Anatidæ or Lamellirostral tribe the 
sternum is thin, but of large size, very convex 
transversely, and much elongated. The keel 
is of moderate depth, and of a triangular form, 
its inferior margin being straight ; there is only 
one fissure on either side posteriorly.* 
In the Divers ( Colymbus) the portion of 
sternum intermediate to the two fissures is pro¬ 
longed beyond the lateral pieces, and the ma¬ 
nubrial process is strongly developed, and of a 
rounded form ; the whole bone is remarkable 
for its length. In the Grebes the sternum is 
characterized by a third mesial fissure of a 
chevron figure intermediate to the two ordinary 
fissures of the posterior margin. 
The sternum of the Cursorial Birds pre¬ 
sents few affinities of structure to that of the 
rest of the class, resembling rather the ex¬ 
panded plastron or abdominal plate of the 
Tortoises. It has neither a keel, nor mantx- 
brial, nor costal processes, and may be com¬ 
pared to a square shield. It is most convex 
in the Rhea, and least so in the Ostrich; 
* The modifications of the sternum in relation to 
the folded trachea will be treated of in the article 
on the Organs of Voice.
        

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