642 



MAMMALIA 



[CH. 



There is no quadrate recognisable as such, the lower jaw con- 

 sisting of a single dentary bone on each side, which articulates with 

 a smooth cup-shaped facet on the squamosal, called the glenoid 

 cavity. Occupying the position of the prefrontal bone in Reptiles 

 is a -small bone called the lachrymal. This bone derives its name 

 from the fact that it is pierced by a hole called the lachrymal 

 foramen (13, Fig. 316) which permits of the passage of a duct 

 leading from the orbit to the cavity of the nose. This duct carries 



FIG. 317. Dentition of a Dog, Canis familiaris xj. 



Second incisor. c. Canine. _P m l> pm4. First and fourth premolars. 

 ml. 



pml, pm4. 

 First molar. 



off the excess of tears (Lat. lacrima, a tear), the secretion of the 

 lachrymal gland, a development of the epidermis between the eyelid 

 and the eye. The lip-bones, the premaxilla and maxilla, are 

 well developed and like the dentary normally bear teeth, all of 

 which are implanted in distinct sockets formed by the upgrowth of 

 the bone which bears them. Many of these teeth are rooted, that 

 is to say, after a certain time the dermal papilla on which the 

 tooth is moulded becomes constricted at the base, so as to be 



