38 



THE HISTORY OF THE PEEYCOSATJRTA, WTTH 



The lachrymals are large plate-like and very thin except at their posterior extremity. 

 Here the orbital portion is thickened and pierced by one or two foramina. Below, the 

 edge becomes very thick and strong and is inserted into the posterior edge of the maxil- 

 lary. The lachrymals form the anterior lower part of the orbit. They are joined to the 

 prefrontals above, the maxillaries in front and below, thejugals behind. 



The jugals (PL I, Fig. 6) are large and take part in the rim of the orbit, forming 

 the lower and part of the posterior edges. The rim is marked by a. sharp, elevated ridge. 

 Below it is divided into two main parts. One running forwards and downwards joins the 

 posterior edge of the maxillary. The inner face of this arm is marked by a strong ridge 

 bearing at its lower edge a strong articular face for the ectopterygoid. The second runs 

 almost straight backward, becomes quite slender posteriorly and joins the quadratojugal 

 by a squamous suture. The whole of the lower portion of the bone becomes quite thin. 

 The upper posterior process is united with the postorbital. The jugals join therefore the 

 following elements: In front the lachrymals, below the maxillaries, behind the quadrato- 

 jugals and above the orbitals. 



The suspensorial region of the skull is composed of four elements : the quadrate, 

 quadratojugal, .squamosal and prosquamosal (PI. I, Figs. 8, ( .), 10). 



The quadrate is peculiarly flat and depressed. It is covered superiorly by the squa- 

 mosal, prosquamosal and quadratojugal. The squamosal, reduced distal ly to a, broad, 

 thin plate, is joined to the upper surface by a squamous suture, covering the inner por- 

 tion. Laterally it wraps around the inner edge of the quadrate and appears largely on 

 the lower face. 



The outer part of the upper surface is covered by the prosquamosal and quadrato- 

 jugal joining it by squamous suture. The prosquamosal lies just external to the squa- 

 mosal, but is soon separated from the quadratojugal, which is wedged in between them. 

 Superiorly the quadrate sends a, process forward which extends between the squamosal 

 and prosquamosal. The anterior end of this projection is incomplete, but possibly was 

 continued forwards to join the posterior plate of the pterygoid. The outer edge of the 

 projection is marked near its origin by a deep pit extending between the quadrate and 

 quadratojugal. It represents the foramen between the quadrate and quadratojugal in 

 Sphemdon, Phytosaurus (Belodon) and Ichthyosaurus. 



The articular face for the lower jaw consists of two grooves lying at a Large angle to 

 the main axis of the skull. The outer is the longest and deepest, the inner wide and 

 more shallow. They extend across the inferior face of the bone from before backwards, 

 and are separated by a ridge as high as the external walls. 



The quadratojugal, as shown by the articular face on the posterior process of the 

 jugal, sent a strong process forwards. Posteriorly the i ir edge extends as a, wedge 



