148 VERTEBRATE ZOOLOGY 



the lower portion of the posterior border of the orbit ; the quad- 

 ratojugal, which is just back of the jugal and forms the front side 

 of the circular opening covered by the tympanic membrane ; the 

 squamosal, a large bone adjoining the parietal, and forming the 

 prominent lateroposterior end of the skull ; the quadrate, which 

 forms the hinder side of the circular tympanic opening and termi- 

 nates below in the articular surface of the lower jaw ; the prootic, 

 a small bone lying between the quadrate and the parietal, and 

 pierced by the foramen of the external carotid artery ; the opis- 

 thotic, a small bone directly back of the prootic and between the 

 squamosal and the supra-occipital ; the epiotic, a small bone which 

 is fused with the lateral edge of the supra-occipital and appears as 

 a part of it, lying in contact with the opisthotic, prootic, and 

 parietal. 



Exercise 24. Make a drawing of the dorsal aspect of the skull on a 

 large scale, showing the outlines of these bones. Carefully label all. 



Study the ventral surface of the skull. The bones which appear in 

 the medial area are the following: the paired premaxillae, which 

 form the anterior end ; the paired maxillae, which are directly back 

 of the premaxillae and with them support the horny biting surface 

 of the jaws ; the median vomer, a slender bone between the max- 

 illae, which helps form the walls of the posterior nares ; the paired 

 palatines, between the hinder ends of the maxillae, which hold the 

 vomer between them and help form the roof of the mouth ; the 

 paired pterygoids, large bones immediately back of the palatines, 

 which meet each other in the median line and help form the roof 

 of the mouth ; the median basisphenoid, immediately back of the 

 pterygoids ; the median basi-occipital, which is back of the basi- 

 sphenoid and forms the hinder end of the skull. Lateral to the 

 hinder end of the pterygoid on each side is the quadrate, back of 

 which is the squamosal ; medial to the hinder part of the last- 

 named bone is the opisthotic, and immediately back of this the 

 exoccipital. Note that the occipital condyle is formed of three 

 portions, and determine the bones of which they are a part. 



Exercise 25. Make a drawing of the ventral aspect of the skull on a 

 large scale, showing the outlines of these bones. 



