138 ZOOLOGY. 



several distinct germs, nuclei, or portions, which, ultimately 

 coalesce. 



These intermaxillary bones which fuse so early in man, 

 remain distinct throughout life in many mammals and others, 

 and form a distinctive feature of the face. They are also 

 called premaxillary (i m Fig. 90). 



In man the germs of the lower jawbone become fused at 

 an early age; in many mammals it is formed of two pieces, 

 united by cartilage at the symphysis of the chin. A brief 

 inspection of the lower jawbone shows its more remarkable 

 points : its articular surface, by which it rests on the glenoid 

 cavity of the temporal; the coronoid process projecting 

 upwards in front of the condyle, and to which is attached the 

 powerful temporal muscle ; the alveolar edge of the jaw, form- 

 ing its dentar portion ; the symphysis or union of the chin, 

 and the base and angle. The masticating muscles are very 

 powerful, especially in the carnivora ; and in some animals 

 the disposition of the muscles rendering the arm of the lever 

 of resistance equal to, or even shorter than that of the power, 

 adds to their strength. 



The hyoid or lingual bones (Fig. 31), placed in front of the 

 neck, representatives of another apparatus, of which in man, 

 mammals, birds, and most reptiles, we have only the rudi- 

 ments, and which only attain their full development in fishes, 

 give attachment to the muscles of the tongue and to others. 

 They are not considered as part of the skeleton, properly so 

 called. 



271. The Trunk, or Torso. The most important part 

 of the skeleton of the trunk is the vertebral column, composed 

 of the bones called vertebrae. It supports the head, which 

 may be considered as a continuation of it ; but anatomists 

 still speak of the vertebral column as a part distinct from the 

 head. In this view it is composed of 33 vertebrae, namely, 



well as other mammals, which early become fused with the maxillary, so that 

 nearly all traces of their early existence are lost. The incisive teeth always 

 appear in these bones in the upper jaw, and whatever be their shape, so long 

 as they belong to these bones are called incisive. Thus the enormous tusks 

 of the elephant are called incisors, notwithstanding their shape and size, 

 simply for this reason, that they grow in the intermaxillary bones. For the 

 same reason we call the gnawing or cutting teeth of the beaver, porcupine, 

 hare, rabbit, incisive teeth, and not merely from their functions. Notwith- 

 standing, it is right to observe that the upper incisors of the rabbit grow 

 from a pulp, the extremity of which is lodged in a small osseous cavity of 

 the upper maxillary bones. They merely pass through the intermaxillary 

 bones, which furnish them no doubt with their chief support, mechanically. 

 It. X. 



