OF COLYMBUS TORQUATUS. 133 



' of the tympanic bone. Just above the optic foramina are two others of considerable 

 size, and of a regular quadrilateral shape. The alse majores form that part of the skull 

 intermediate between the zygomatic portion of the temporal and posterior orbital pro- 

 cesses of the frontal. 



Parietal. The complete anchylosis of the roof of the cranium leaves no traces of the 

 original margins of these bones. The space which represents them is bounded posteriorly by 

 the elevated crest marking the edge of the occipital, below and behind by the temporal, 

 below more anteriorly by the alee majores ; on the roof of the skull they may be con- 

 sidered as projecting about as far forward as a line drawn between the two posterior orbital 

 processes of the frontal. The space thus included is for a little distance on the anterior 

 portion smooth, and covered only by the skin ; but by far the greater portion of the bones 

 form on either side rough, irregular, greatly depressed fossa?, generally styled the " temporal 

 fossa?." These are entirely filled up, in the recent state, to the level of the rest of the skull by 

 the temporal and masseter muscles. The two fossa? are separated from each other by a well- 

 marked median longitudinal crest, from the anterior extremity of which two other equally 

 elevated ridges proceed on either side to the posterior orbital processes, and form the 

 anterior boundaries of the fossa?. 



Temporal. This bone forms the infero-posterior angle of the skull, being situate between 

 the parietal, occipital, and sphenoid. Superiorly, the "squamous" portion sends forward 

 and downward the zygomatic process. The mastoid process seems to be indicated in that 

 part of the bone which is continuous with the condyloid process of the occipital; it gives 

 origin to the analogue of our digastricus. The petrous portion of the bone containing the 

 osseous elements of the organ of hearing, lies internally on the inferior aspect of the skull, 

 anchylosed with the side of the occipital basilar process. To the under surface of the 

 zygomatic process is articulated the movable element of the temporal. 



Os pcdiccllatvm. This, the tympanic element of the temporal bone, articulates, by two 

 separate, oval, very convex facets, placed side by side in a line oblique to the axis of the 

 body, with two corresponding deeply concave depressions at the bottom of the fossa on the 

 under surface of the zygomatic process. The depth of the depression in which the head of 

 the pedicellate bone is received, together with a projecting border from the edge of the 

 zygomatic process, tends to make the joint a very strong one. 



From this articulating head the bone projects directly downwards and a little forwards 

 for about three fourths of an inch. It first sends off its orbital process, — a stout compressed 

 process of bone, projecting directly forwards and upwards into the orbit. This process has 

 a considerable upward curve ; its superior margin being concave, and running up quite to 

 the head of the main bone ; its inferior margin is convex, and merges into the main bone 

 a little above the temporo-maxillary articulation. The top of this process is rough, for 

 muscular attachments. 



After giving off this orbital process, the bone becomes a little constricted into a " neck," 

 upon which is supported the broad, irregularly shaped, and uneven head for articulation 

 severally with the pterygoid, malar, and inferior maxillary. 



The pterygoid facet is placed on the side of the head of the bone, just internal to, and 

 below, the root of the orbital process. It is a single, obliquely elongated, smooth, very 

 convex tubercle pointing inwards and forwards, on which the concave head of the pterygoid 

 bone is placed. It presents something of the characters of the ball-and-socket joint, 

 although rotation in all directions is not equally perfect. 



