xin PHYLUM CHORDATA 297 



(para), corresponding to the bone of the same name in the Frog, 

 and Trout, but here much reduced in size and importance, and 

 ankylosed with the basi-sphenoid. 



In the wall of the auditory capsule are three ossifications 

 pro-otic, epi-otic and opisthotic (op. ot). The first remains distinct, 

 the second becomes merged in the supra-occipital, and the third 

 in the ex-occipital. The ex-occipital and opisthotic are produced 

 outwards as a pair of prominent horizontal processes, the parotic 

 'processes. 



The large orbits are closely approximated, being separated 

 only by a thin vertical inter-orbital septum. The cranial cavity 

 is roofed over by the parietals (par) and frontals (fr). The former 

 are united together ; in the middle is a small rounded aperture 

 the parietal foramen (par./). The frontals remain separated from 

 one another by a median frontal suture : between them and the 

 united parietals is a. transverse coronal suture. The nasal cavities are 

 roofed over by a pair of nasals (nas). A small pre-frontal (pr.fr.) 

 lies in front of the frontal, and helps to bound the orbit anteriorly, 

 and another small bone the lacrymal (Icr) perforated by an aper- 

 ture for the lacrymal duct, lies at the anterior extremity of the orbit, 

 just within its border. A row of small bones the supra-orbitals 

 (s. orb) bounds the orbit above, and behind is a post-orbital (pt. 

 orb) articulating with the frontal. Just behind the latter are two 

 supra-temporal bones (supra t l , supra t 2 ), in close relation to which 

 is the squamosal (sq). At the anterior extremity of the snout is a 

 median bone formed by the coalescence of the two pre-maxillw 

 (p. mx) ; this bears the four anterior teeth of each side. On each 

 side behind the premaxilla is the maxilla (max), consisting of two 

 portions, an alveolar bearing all the rest of the teeth, and a palatine 

 extending inwards on the roof of the mouth, together with an 

 ascending process articulating with the nasal and pre-frontal 

 above. Articulating behind with each maxilla is a jugal (ju) 

 which forms the posterior half of the ventral boundary of the orbit. 

 The quadrate (qu) articulates movably with the parotic process, 

 and bears at its distal end the articular surface for the mandible. 



In the anterior portion of the roof of the mouth, articulating 

 in front with the pre-maxillae and maxillae, are the vomers (vom). 

 Behind them and embracing them posteriorly are the flat palatines 

 (pal). The elongated ptery golds (pt.g) articulate in front with the 

 posterior extremities of the palatines: behind each articulates 

 with the corresponding basi-pterygoid process (has. ptg) of the basi- 

 sphenoid ; and sends back a process which becomes applied to the 

 inner face of the quadrate. A stout bone which extends between 

 the maxilla externally and the pterygoid internally is termed the 

 transverse (trans). Extending nearly vertically downwards from 

 the pro-otic to the pterygoid is a slender rod of bone, the epi- 

 pterygoid (col). 



