426 



THE DOG. PHYLUM CHORDATA 



the auditory capsules posterolateral to the cranium, and the nasal 

 capsules in front. The optic capsules, which are present in the 

 embryo, are reduced in the adult to some cartilage in the sclerotic 

 coat of the eye. In adult mammals almost the whole skull is 

 bony. The cartilaginous cranium is ossified to form a number of 



Fig. 337. — The lower surface of a dog's skull. — From Thomson. 



o.c, Occipital condyle ; B.O., basioccipital ; T., tympanic bulla ; ni.c, postglenoid process behind fossa or 

 condyle of mandible ; B.S., basisphenoid ; P.S., base of presphenoid ; V., vomer ; M.2, second molar ; 

 A/. I, first molar; Pw.1-4, premolars, the 4th the large camassial ; c, canine; /.1-3, incisors; 

 Pmx., premaxilla ; mx., maxilla ; Pal, palatine ; /., jugal ; A.S., alisphenoid ; Pt., pterygoid ; Sq., 

 squamosal (the reference line points to the glenoid fossa). 



bones which are joined to each other by jagged edges called 

 sutures. At the posterior end, surrounding the foramen magnum, 

 the hole through which the spinal cord passes to merge with the 

 brain, are four, a basioccipital below, a supraoccipital above, and 

 an exoccipital on each side. The exoccipitals make two knobs, the 

 occipital condyles, which articulate with the first vertebra ; a 

 small part of each condyle is formed from the basioccipital. In 

 front of the basioccipital the floor of the cranium is made by the 



