114 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



teeth; maxillae, the large bones at the sides of the nasal bones, and also bearing 

 teeth; jugal or malar, the elongated bones forming the lower boundaries of the 

 orbit and meeting the postf rentals at the middle of the postorbital bar; and 

 quadratojugal, a slender, obliquely placed bone forming the posterior boundaries 

 of the lateral temporal fossae. The quadrate is a stout bone obliquely placed 

 between the quadratojugal and the exoccipital. The posterior end of the quad- 

 rate has a concave surface for articulation with the lower jaw. 



Turn the skull over and identify the same bones of the maxillary arch from 

 below. Premaxillae and maxillae form the anterior half of the ventral surface, 

 meeting in the median line. Between the two premaxillae is the small anterior 

 palatine vacuity. Posterior to the maxillae in the median region and forming 

 the inner boundaries of the posterior palatine vacuities are the palatines. Pos- 

 terior to the palatines are the broad pterygoids which inclose the posterior nares. 

 Extending from the sides of the pterygoids to the posterior end of the maxillae 

 are the ecto pterygoids or trans palatines. 



All of these bones of the upper jaw except the quadrate are membrane bones. 

 The quadrate represents the ossified posterior end of the pterygoquadrate carti- 

 lage. The quadrate articulates with the lower jaw, as in the majority of 

 vertebrates. 



4. The occipital region. This region forms the posterior end of the skull 

 and consists of four cartilage bones derived from the parachordal cartilages. 

 Turn the skull so that its posterior end faces you. The foramen magnum is 

 bounded by three bones, one on each side, the exoccipitals, and one below, the 

 basioccipital. The basioccipital bears most of the large rounded occipital condyle 

 but both exoccipitals send down processes which take part in the condyle. Above 

 and between the two exoccipitals is the triangular supraoccipital, which articulates 

 with the posterior end of the parietal. 



5. The bones of the otic capsule. There are three of these surrounding the 

 external auditory meatus and inclosing the ear. They are named the epiotic, 

 the opisthotic, and the prootic. The first of these is fused with the supraoccipital ; 

 the second with the exoccipital; the third alone remains distinct in the adult. 

 They are difficult or impossible to see in external view. To find the prootic, 

 turn the skull sidewise so as to obtain a profile view, and identify a large foramen, 

 the foramen ovate, just below the supratemporal fossa. The posterior wall of 

 this foramen is formed by the prootic bone, which articulates with the quadrate 

 bone behind, the suture between the two occurring at the external rim of the 

 foramen. The otic bones are of course cartilage bones, formed in the otic capsule. 



6. The posterior sphenoid region. This region is anterior to the occipital 

 region and forms the floor of the cavity occupied by the brain. Turn the pos- 

 terior end of the skull toward you and identify the V-shaped end of the 

 basisphenoid, between the basioccipital and the pterygoids. Most of the basi- 

 sphenoid is concealed from view by the pterygoids and the quadrates, but its 



