24 ANATOMY OF THE RAT 



behind the body. Three processes are attached to its pos- 

 terior end. The coronoid process projects dorsally into the 

 orbito-temporal fossa. Just behind this is the condyloid 

 process, bearing an elongated rounded knob which articu- 

 lates with the mandibular fossa of the squamosal bone. 

 These articular surfaces in the rodent permit anteropos- 

 terior motion of the jaw. The angular process is directed 

 posteriorly. The anterior mandibular incisure is a pro- 

 nounced depression separating the coronoid from the con- 

 dyloid process. The posterior mandibular incisure like- 

 wise separates the condyloid and angular processes. The 

 mandibular foramen lies at the base of the condyloid 

 process. The mental foramen lies ventroanteriorly to the 

 molar teeth. Other foramina occur on the surface of the 

 mandible. A ridge extends on the lateral surface of the 

 mandible from the mental foramen backward to the border 

 of the angular process. The medial surface of this process 

 is concave. The incisor tooth of the lower jaw, like that 

 of the upper, is sickle-shaped, and inserted in a large 

 dental alveolus which extends caudally, ventral to the 

 molar teeth, nearly to the base of the condyloid process. 

 The mandible is largely a membrane bone. 



Hyoid Bone (Os Hyoideum) 



The hyoid is a u-shaped bone at the base of the tongue 



composed of a slender transverse body and two pairs of 



horn^ (cornua), one pair extending anteriorly, the other 



pair posteriorly. 



Exercise IV. Make a labeled sketch of each of the bones of the 

 head. 



THE VERTEBRAL COLUMN 



The vertebral column, or backbone, is the second division 

 of the axial skeleton. It is a linear series of numerous 



