430 



THE DOG. PHYLUM CHORDATA 



a.c. — 



In front of the maxilla is a smaller premaxilla, which completes 

 the face and palate, surrounds, with the nasals, the external 

 nostrils, and meets its fellow in front and below. This type of jaw 



suspension, in which the upper jaw is 

 intimately joined to the cranium, is 

 called autostylic (p. 583). 



The cartilaginous lower jaw, known 

 as Meckel's cartilage, entirely dis- 

 appears in the adult except for two 

 posterior fragments of it which have 

 become ossified as the malleus. It is 

 functionally replaced by a single mem- 

 brane bone, the dentary. This is loosely 

 sutured to its fellow in front, and 

 posteriorly has three conspicuous 

 processes : an ascending coronoid, to which the muscles which 

 close the mouth are largely attached, an angular at the lower 

 corner, and between these an articular. This last is shaped like a 



'p.c.-- 



FiG. 339. — The hyoid bone 

 of a rabbit, from above. 



a.c, Base of the anterior comu ; b., 

 body ; p.c, posterior comu. 



Fig. 340. — A diagram of the skull bones of a mammal (partly after Flower and 



Weber), the membrane bones shaded. 



B.O., Basioccipital ; E.O., exoccipital ; C, condyle ; S.O., supraoccipital ; Par., parietal ; Fr., frontal ; 

 Na., nasal ; Pmx., premaxilla ; M.E., mesethmoid ; L., lacrimal ; Tu., turbinal ; P.S., presphenoid ; 

 O.S., orbitosphenoid ; A.S., alisphenoid ; B.S., basisphenoid ; SQ., squamosal ; P., periotic ; T., tym- 

 panic ; PI., palatine ; Pt., pterygoid ; Mx., maxilla ; Ju., jugal ; T.H., tympanohyal ; S.H., stylohyal ; 

 E.H., epihyal ; C.H., ceratohyal ; B.H., basihyal ; Th.H., thyrohyal ; vomer ; MN., dentary. 



roller, and fits into the hollow in the squamosal. The result of 

 this type of articulation is that although the mouth can be widely 

 opened it cannot be moved from side to side without dislocation. 

 The remainder of the ventral part of the skull is represented by 

 the hyoid apparatus, and some cartilages on the larynx (p. 446). 

 The hyoid, which is below the tongue, is shown in Fig. 339. 

 The skull of the dog is complete, that is, there are no places 



