AVES. 



283 



(Upupa), 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,fig. 129;. 



In the Trogons, Hollers (Coracius)j 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 

 Hap tores, being in some species 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- 

 aessorial 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 

 ridges 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 procqsses are prolonged 

 upwards and forwards; the posterior lateral 



processes pass backwards exterior to the 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 Ardeida: 

 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 tissure 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, the 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 

 ou either side. In the Penguins, these fissures 

 are of considerable extent (J\J\fg> 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 Anatidee 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 manu- 

 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. 



