MAMMALIA. 635 



These pieces are generally consolidated : by their lateral margins 

 they give attachment anteriorly to the clavicles, if these bones be 

 present ; and, behind these, to the costal cartilages of the true ribs. 



From the whole arrangement of the thorax, it is evident that 

 the ribs are capable of extensive movements of elevation and de- 

 pression, whereby the capacity of the whole thoracic cavity may be 

 increased or diminished ; movements which, aided by those of the 

 diaphragm, draw in and expel the air used for respiration. 



(716.) The anterior extremity is appended to a broad scapula, 

 generally unconnected with the rest of the skeleton except by 

 muscular attachments. In quadrupeds that use this extremity as 

 an instrument of prehension or of flight, a clavicle is interposed 

 between the scapula and the sternum ; but most frequently this ele- 

 ment of the shoulder is deficient, and even the coracoid bone, if a 

 vestige of it remains at all, is reduced to a mere appendage to the 

 scapula, known to the human anatomist as the coracoid process. 

 The rest of the limb presents the arm, the fore-arm, the carpus, 

 metacarpus, and phalanges ; but these are so altered in appearance 

 in different orders, that no general description will suffice, and we 

 must therefore defer this part of our inquiry ^frr tho present. 



(717.) In the posterior extremity there is equal dissimilarity in 

 the construction of the distal portions of the limb ; but the pelvis, 

 although much modified in form, consists of the same pieces as in 

 the human subject, and in like manner has the pubic arch and fora- 

 mina fully completed. 



(718.) The cranium and face are made up of numerous bones, 

 easily recognizable, as they correspond in their general arrangement 

 with those composing this part of the skeleton in the lower Verte- 

 brata. Their developement in the facial region is large in propor- 

 tion to the strength of the muscles moving the lower jaw; and they 

 are so disposed as to form buttresses to resist the powerful pressure 

 of the teeth, as well as to enclose cavities wherein are lodged the 

 organs connected with the senses of smell and of vision. One 

 example will answer our present purpose, and we have selected the 

 skull of the Pig as one calculated to show a medium develope- 

 ment of the whole series. 



In the face we find on each side two bones entering into the 

 composition of the upper jaw, into which teeth are implanted ; 

 these are the superior maxillary (fig- 94, 18), and the intermaxil- 

 lary (17). These bones, moreover, bound extensively the cavity of 

 the nose ; and, together with the palatine process of the palate 



