858 AMPHIBIA. 



The orbito-sphenoid (fig. 32) is a moderately elongated bone, with its inner side 

 smooth and concave, and its outer side transversely convex. It is perforated near 

 its posterior extremity by a large foramen directed upwards for the transmission of 

 the optic nerve and by a small one immediately behind the former. The anterior 

 and upper extremity which forms the internal lateral margin of the internal nostril 

 is marked by two processes which enclose a rather deep groove. It articulates with 

 the prefronto-lachrymal, exoccipital, parasphenoid, palato-vomerine, and parietals. 



The temporal (fig. 35) is directed obliquely outwards and slightly backwards, 

 which partly accounts for the wide gape of this animal. It rests on the anterior 

 external angle of the auditory capsule and touches the parietal and the frontal 

 anteriorly, completing the upper margin of the arch of the orbit. Its anterior angle 

 receives the head of the pterygoid, which also rests on the process on the under side 

 of the auditory capsule external to the supposed orifice of the facial nerve. It is a 

 hammer-shaped bone with a massive head projecting behind, consisting almost 

 entirely of the rough, hard, bony substance of the cranial crest. 



The quadrate (fig. 35) is somewhat triangular, with the longest diameter of its 

 articular facet lying obliquely across the long axis of the temporal, concave outwards 

 and backwards, the face of the facet looking outwards and forwards. A prominent 

 process surmounts the back of the facet, and a curved one is directed forwards for 

 articulation with the posterior end of the maxilla. 



ThQ pterygoid {fi^. 36) consists of two parts, a body and a wing-like process 

 projecting forwards from its anterior margin. The body of the bone is applied to 

 the internal surface of the temporal and quadrate, and by its head to the auditory 

 capsule and to the inner side of the angle of union of the maxillary process and body 

 of the temporal. 



The head consists of two parts corresponding to its articulations, an internal 

 and external. The former is hollowed out, and the cavity opens on the external side 

 of the neck of the bone, and is prolonged along the posterior margin of the body as 

 a well-defined short groove which is converted into a canal when the bone is in 

 position against the temporal which closes it below. A branch of the cavity is also 

 prolonged along the wing as a groove in some skulls, and a canal in others, and when 

 the latter exists, it communicates with the head of the bone by a special foramen. 

 Superiorly the cavity is closed by the pterygoid process of the auditory capsule. 

 The anterior wing of the bone is hard and somewhat sickle- shaped, and is projected 

 forwards and outwards to touch the maxilla, when it sends backwards a narrow 

 shelf of bone from the inner margin of the internal nares. 



The floor of the cranial cavity is almost perfectly straight (fig. 33), although 

 the outline of the skull is much curved ; the curvature, however, is confined to the 

 roof which arches down over the anterior extremity of the parasphenoid until the 

 anterior margins of the f rentals are brought nearly on a line with that bone. A line 

 prolonged forwards from the parasphenoid would have the premaxillaries below it. 



The extremities of the hyoid arch (fig. 40), when the mouth is closed, project 

 backwards and upwards behind the skull, on a line with the lateral cranial crest. 



