ANATOMY OF VERTEBRATES. 139 



seat of much greater modifications, by which they are made sub- 

 servient to a variety of functions unknown in the haemal arches of 

 the rest of the body. Thus the two anterior haemal arches of the 

 head perform the office of seizing and bruising the food ; are 

 armed for that purpose with teeth : and, whilst one arch is firmly 

 fixed, the other works upon it like the hammer upon the anvil. 

 The elements of the fixed arch, called ' maxillary arch,' fig. 93, H, 

 iv, have accordingly undergone the greatest amount of change, in 

 order to adapt that arch to its share in mastication, as well as for 

 forming part of the passage for the respiratory medium which 

 traverses it. Almost the whole of the upper surface of the max- 

 illary arch is firmly united to contiguous parts of the skull by 

 rough or sutural surfaces, and its strength is increased by bony 



94 



Section of cranium, Crocodile 



appendages, which diverge from it to abut against other parts of 

 the skull. Comparative Anatomy teaches that, of the numerous 

 places of attachment, the one which connects the maxillary arch by 

 its element, 20, with the centrum, 13, and with the descending plates 

 of the neurapophyses, 14, of the nasal segment, is the normal or 

 the most constant point of its suspension ; the bone, 20, being the 

 pleurapophysial element of the maxillary arch : it is called the 

 ' palatine,' because the under surface forms a portion of the bony 

 roof of the mouth, called the ' palate,' as in fig. 98 c, 20. It is 

 articulated at its fore part with the bone, 21, which is the hanna- 

 pophysial element of the arch. This bone is called the ' maxil- 

 lary,' and is greatly developed both in length and breadth, fig. 

 95, 21 : it is connected with 20, figs. 94, 98 C, behind and 

 with 22 in front, which are parts of the same arch, and with 

 the diverging appendages of the arch, viz., fig. 95, 26, the malar 

 bone, and fig. 98 c, 25, the ectopterygoid : the maxillary is also 

 united with the nasals, 15, and the lacrymal, 73, as Avell as 

 with its fellow of the opposite side. The smooth, expanded 



