116 TSE BONES. 



The zygomatic hones have the form of two very thin stylets, and are uuited to the square 

 bone by their posterior, and consolidated with the supermaxillary by their anterior 

 extremity. Tlie vomer separates the guttural openings of the nose from one another. 



The bones of the upper jaw are not fused with each other so rapidly as the bones of 

 the cranium. The ascending processes of tlie premaxillary and nasal bones even remain 

 for a long time united to the frontal bone by a simple synarthrodia! articulation. This 

 arrangement allows the upper beak to execute a certain elevating movement, of whicli 

 we will speak wlien describing the articulations. 



The inferior maxillary hone is originally formed of a great number of distinct seg- 

 ments whioli are soon united into a solid piece. The square, petrous, or bone of tlie 

 tympanum ought to be considered as detached from tlie temporal. It is prismatic in 

 shape, and provided on its upper surface with a diarthrodial facet which unites it to the 

 temporal, and on its lower face with another fiicet articulating with the branch of the 

 maxilla. Outwards it joins the zygomatic bone, and inwards with the pterygoid.' 

 Behind, it gives attachment to the membrane of the tympanum; and in front it 

 presents a small eminence of insertion which Meclcel considered a second zygomatic 

 process. 



Thorax. — Sternum (fig. 73, h). — The sternum of birds, serving as a basis of support lo 

 the muscles moving the wings, should offer, and does in fact show, a remarkable degree 

 of strength, because of the extraordinary volume of these muscles. And these being more 

 powerful and energetic as the bird exhibits a greater degree of aptitude for flight, it results 

 that the structure of the sternum is solid in proportion as the bird is strong on the wing. 

 For this reason we may infallibly pronounce as to the extent and power of a bird's flight 

 by an inspection of the sternum of individuals of its species. In this respect, however, we 

 only announce what is well known to be a particular application of the rules established 

 by the great law of concordance between the anatomical disposition of organs and their 

 physiological finality. 



Studied in Palmipedes, which will serve as a type for description, the sternum presents 

 itself in the form of a large rectangular cuirass, elongated from before to behind, of itself 

 constituting the inferior wall of the thoracic cavity, and also largely protecting the 

 abdominal cavity. Its superior face is concave, while the inferior is convex, and entirely 

 occupied by the insertion of the pectoral muscles. It presents, on the median line, a 

 thin and very sa,lient ridge, named the hrislcet (or heel), which in a remarkable manner 

 multiplies the points of attachment of these muscles. The anterior border offers in its 

 middle a small eminence of insertion, the episternal. Laterally, two articular grooves 

 are seen which correspoml to the coracoids. The posterior border is cut by two notches 

 which are often converted into foramina. On the lateral borders are observed small 

 double articular facets answering to the inferior ribs. The angles which separate these 

 two borders from the anterior are both prolonged into a little eminence, named by some 

 authors the costal process. 



In the Fowl, the sternum is not so strong as in the Qoose or Duck. On each side of 

 the brisket it shows two wide notches, which greatly reduce its substance. These 

 notches, closed in the fresh state by membranes, are distinguished as external and 

 internal. The latter, of greater size than the former, extends nearly to the extremity of 

 the bone. From this division of the lateral plates of the sternum result two long and 

 slender processes directed backwards. The external terminates by becoming widened, 

 and forming a kind of bony plate, which covers the last inferior ribs. 



The sternum of Pigeons is distinguished by the enormous development of the brisket. 

 The two notches of the fowl are also met with in these birds, but the internal is nearly 

 always converted into a narrow foramen. 



This comparative study of the sternum in the chief domesticated birds leads us to 

 appreciate the correctness of the principles just enunciated, witli regard to the form and 

 extent this bone may exhibit. The Gallinaceous Birds, properly bo called, which fly 

 little and badly, have the sternum singularly weakened by the deep notches cut in its 

 lateral parts. With Palmipedes, the sternum is wide and but slightly notched, so that 

 the goose and duck, which waddle along so awkwardly in our poultry yards, are capable 

 of sustaming long and rapid flight, like that of the wild individuals of the same species. 

 With regard to Pigeons, which are well known to be swift and powerful flyers, may this 

 advantage not be due to the extiaordinary development of the keel which constitutes the 

 brisket ? 



Ribs. — In the Fowl and Pigeon there are seven pairs of ribs ; and in the Buclc nine 

 pairs. Articulated superiorly with the dorsal vertebra;, as in mammals, these bones are 

 provided near their middle with a flat eminence which commences at the posterior 

 border, and is directed backwards and upwards to rest by its free extremity on the 

 external face of the next rib. These eminences (Fig. 73, 20} form an epiphysis at an 



