162 THE BONES. 



which represent the two small premaxillaries of Mammals. This bone is very 

 considerable, and of itself forms the base of the upper beak, the form of which it 

 determines ; it is pointed and conical in the GalUnacea, and wide and flattened 

 above and below in Palmipedes. In front it circumscribes the external openings 

 of the nose, and is prolonged superiorly into two lengthy processes which dovetail 

 between the nasal bones. Two inferior processes belonging also to this bone 

 concur in the formation of the palatine roof. The supennaxillaries, analogues of 

 the supermaxillaries of Mammals, are two rudimentary bones situated on the sides 

 and at the base of the beak. They form a part of the palatine roof and the walls 

 of the nasal cavities. The nasal bones circumscribe above, inwardly, and even 

 outwardly, the external orifices of these cavities. The palatine hones encircle, as 

 in Mammals, the guttural openings of the nose, and constitute in great part the 

 roof of the palate ; their posterior extremity lies against the pterygoids ; the 

 anterior joins the supermaxillaries and the inferior process of the premaxillary 

 bone. The pterygoids extend obliquely from the sphenoid to the square bones, 

 and are united to the sphenoid by diarthrodial articulation. The zygomatic hones 

 have the form of two very thin stylets, and are united to the square bone by their 

 posterior, and consolidated with the supermaxillary by their anterior, extremity. 

 The vomer separates the guttural openings of the nose from one another. 



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

 bones of the cranium. The ascending processes of the premaxillary and nasal 

 bones even remain for a long time tmited to the frontal bone by a simple 

 synarthrodial articulation. This arrangement allows the upper beak to execute 

 a certain elevating movement, of which we will speak when describing the 

 articulations. 



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

 segments, which are soon united into a solid piece. The square, petrous., or hone 

 of the tympanum ought to be considered as detached from the 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 facet articu- 

 lating with the branch of the maxilla. Outwards it joins the zygomatic bone, 

 and inwards the pterygoid. Behind, it gives attachment to the membrane of 

 the tympanmn ; and in front it presents a small eminence of insertion, which 

 Meckel considered a second zygomatic process. 



Thokax. — Sternum (Fig. 109, H 1). — The sternum of Birds, serving as a 

 basis of support to 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 creature 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 appli- 

 cation 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. 



