Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/725

TIG. 15. Same skull, side view, X 3 diameters. Letters as above, with the

addition of p., parietal, </., dentary, su., surangular, a., angular, p.a.p., posterior angular process; i.a.p., internal angular process; ar., aiticulare.

The large quadrate bone (figs. 13 and 15, q.) has its free pedicle or orbital process still soft above. Its otic process has a larger rounded head for the squamosal ($<!.}, and a lesser rounded head for the prootic within. In front of the otic process is a sort of trochanter or spur. Below, the articular facet is somewhat divided, by a shal low fossa, into an outer larger and an inner lesser facet. The otic process passes through the front of the tympanic cavity (first cleft), and becomes involved in the membrane thereto attached, namely, the membrana tympani. It was mistaken by anatomists of the last generation for the true tympanic bone. Behind this bone (see fig. 13) there are seen two holes, the inner of them leads to the auditory f enestrse (ovalis and rotunda), and the outer is the opening into a gallery which communicates, by means of diploe, with one on the other side. These are the " upper tym panic recesses," and have their counterparts in the Croco dile. Besides the pterygoid and palatine, in that part of the mandibular arch which i folded over the mouth, for the first post-oral enfolds itself to make all the lower and much of the upper jaw, there are in the outer part of the maxillo-palatine process three bones formed on each side, as we have seen.

The first of these is the bony ichthyic maxillary (mx.), with a bony foot, that grows inwards and backwards in a falcate manner, to articulate with the sides of the fore-end of the vomer. These are the maxillo-palatine processes (mx.p.) Behind the maxillary, overlapping its jugal pro cess, is the styloid jugal (/) ; and behind this, and over lapping it, the quadrato-jugal, which is hooked to fit in the side of the base of the quadrate behind (q.j., q.) There is a small joint cavity at this place,

The side view (fig. 15) illustrates the above description; but it also ehows much that is not visible below. The section (fig. 16) helps us still further.

op., opisthotic; a.s.c., anterior semicircular canal; s.c., sinus canal; $p.,

splenial bone. The small bony centre between the prootic (pro.) and the super-occipital (t.o.) is the epiotic.

The roofing bones are now well seen; the largest of

these are the frontals (/!), which form the upper crescent of the large circle of the eye. They flatten in front, -where they are overlapped by the nasals and nasal processes of the premaxillaries (n. px.) a peculiarly ornithic character amongst the higher vertebrata. The orbital rim is very neat and perfect ; the main part of the bone, covering the hemisphere, is a convex radiating scale. Inside the orbit the bone sends inwards a thin scooped orbital process (/.), on whose convex surface the sloping brain rests. This fails to invest the fontanelle, and the orbito-sphenoid=, as yet, are not. The somewhat oblong and also convex parietals (p.) stop up the gap as far as to the occipital arch ; they are much smaller than the frontals. Both the parietals and frontals are flanked and in some degree over lapped by the squamosals (sq. ), which are more irregular in shape than, but are fully as large as, the parietals. Half the inner face is seen within (fig. 16, sq.); the whole upper edge behind is hidden in this view, and much of the lower part, which forms a strong eave over the huge ear- mass. The lower edge has a cup for the quadrate main head. On the outside (fig. 15) there is to be noticed a variable cartilaginous tract ; it takes in all the elegant crescentic tympanic wing of the exoccipitals (t.e.o.), and also runs in front of and between the ex- and super-occipitals (e.o.,s.o.) Between the two bones is the posterior opisthotic region ; in front of the exoccipital is the epiotic region. From the inside the imbrication of the cranial and auditory bones is seen to be very regular and remarkable. Kunning round and across, behind and below the posterior margin of the frontal, we see the fenestrate alisphenoid (a.s.) underskirt- ing the orbital plate of the frontal, then the hollowed inner face of the squamosal, and behind and above that the scooping of the parietal. Below the same, and also

behind it, we have above, two bones, the prootic in front