140 ANATOMY OF VERTEBRATES. 



horizontal plate, which effects the latter junction, is called 

 the palatal plate of the maxillary, fig. 98 c, 21 ; the thickened 

 external border, where this plate meets the external rough surface 

 of the bone, and which is perforated for the lodgment of the 

 teeth, is the ( alveolar border.' The haemal spine or key-bone of 

 the arch, 22, is bifid, and the arch is completed by the symphysial 

 junction of the two symmetrical halves ; these halves are called 

 f premaxillary bones : ' these bones, like the maxillaries, have a 

 rough facial plate, fig. 95, 22, and a smooth palatal plate, fig. 98 c, 

 22, with the connecting alveolar border. The median symphysis 

 is perforated vertically through both plates ; the outer or upper 

 hole being the external nostril, fig. 95, 22, the under or palatal 

 one being the premaxillary aperture, fig. 98 C, p. 



Both the palatine and the maxillary bones send outward and 

 backward parts or processes which diverge from the line of the 

 haemal arch, and give attachment to distinct bones, which form 

 the ' diverging appendages ' of the arch, and serve to attach it, as 

 do the diverging appendages of the thoracic haemal arches in the 

 bird, to the succeeding arch. 



The appendage, 24, called ' pterygoid,' effects a more extensive 

 attachment, and is peculiarly developed in the Crocodilia, As it 

 extends backward it expands, unites with its fellow both below 

 and above the nasal canal, encompassing it so as to form the hinder 

 or palatal nostril, fig. 98 C, n ; the coalesced pterygoids articulate 

 anteriorly with the divided vomer, the palatines, and the basi- 

 pre-sphenoid : posteriorly each broad wing, extending outward, 

 gives attachment to a second bone, ib. 25, called l ectopterygoid,' 

 "which is firmly connected with the maxillary, 21, the malar, 26, 

 and the postfrontal, 12. The second diverging ray of the maxil- 

 lary arch is of great strength ; it extends from the maxillary, fig. 95, 

 21, to the tympanic, 28, and is divided into two pieces, the malar, 

 26, and the squamosal, 27 ; both of which begin to assume more 

 lengthened and slender proportions than in the Turtle (compare 

 fig. 95 with 91). Such are the chief Crocodilian modifications of 

 the hamial arch and appendages of the anterior or nasal vertebra 

 of the skull. 



The hamial arch of the frontal vertebra, fig. 92, H, iii, is 

 someAvhat less metamorphosed, and has no diverging appendage. 

 It is slightly displaced backward, and is articulated by only a 

 small proportion of its pleurapophysis, 28, to the parapophysis, 12, 

 of its own segment ; the major part of that short and strong rib 

 articulating with the parapophysis, 8, of the succeeding segment. 

 The bone, fig. 95, 2$, called 'tympanic,' because it serves to support 



