FOSSIL AND RECENT 

 EHhm 



103 



dpal 



eart 



10mm 



Fig. 50. Osmeroides lewesiensis (Mantell). Hyopalatine bones, opercular series (stippled) 

 and mandible of the left side in medial view. Composite of several B.M.N.H. specimens. 



plate bears numerous small villiform teeth of regular size. The vomer bears a large 

 tooth plate which is partially divided into lateral halves ; the teeth are similar to 

 those on the parasphenoid. 



Hyopalatine bones. The hyopalatine bones are stout and firmly united to one 

 another, forming a rigid roof to the buccal cavity. 



The hyomandibular is broad and articulates with the neurocranium by a large 

 head which is separable into swollen anterior and posterior regions. The lateral 

 surface is marked by two ridges which originate from the articulatory regions and 

 converge ventrally to form a single stout ridge running the length of the hyomandi- 

 bular shaft. The medial surface of the hyomandibular is marked by a prominent 

 groove which leads ventrally to a large foramen. This in turn leads to a canal 

 opening beneath the opercular process on the posterior edge. The groove, foramen 

 and canal mark the path of the hyomandibular trunk of VII and the efferent hyoidean 

 artery. Anteriorly the head of the hyomandibular is produced as a thin wing which 

 is partially covered ventrally by the metapterygoid. 



The metapterygoid is large and irregularly shaped. Posteriorly and ventrally it 

 lies in the vertical plane but antero-dorsally it twists horizontally to lie in con- 

 tinuity with the endopterygoid. Contact with the quadrate was mediated by 

 cartilage, but with other bones union was syndesmotic. Dorsally, where it overlaps 

 the hyomandibular, a cup-shaped depression is formed which received part of the 

 levator arcus palatini muscle. 



The quadrate is fan-shaped and has a deep ' V '-shaped notch which received the 

 pointed end of the symplectic. The anterior border of the quadrate is thin and fits 



