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Show 270 EXPLOitATION OF THE OAN"ONS OF THE OOLORADO. Viewed from behind, the occipital surface is seen to be nearly plane and vertical, with some beveling of the lateral (mastoid) portions. The most remarkable feature is the extent of this surface which is formed by t~e mas· toid. In Geomys, at any rate, the mastoids take as much part in the occipital surface as the occipital hone itsel£ The upper border of this smface is a nearly regular arch from one squamosal angle to the other. The lower outline is likewise a curv.e, with its convexity downward, but its regularity is broken by the nick of the foramen magnum in the middle, the protuberance of the condyles next, similar paroccipital processes next, and after a little interval the mastoid processes. Barring these irregularities of detail the general. occipital surface is elliptical in shape. In the middle, and nickin~ the l~wer hmb of the ellipse, is the foramen magnum, nearly all of which is vertiCal, and consequently not foreshortened in this view. Viewed from below, the general contour is substantially like that presented from the opposite inspection, and we need only attend t ..1 t ·1 'rl fi £' • • • • 0 ue al s. 1e. r t •eature Is the mctstve foramina-very small slits lying wholly in the mtermaxillnry bones, yet nearer to the molars than t th · · • 0 e InCISOrS, SO great IS the production of the rostrum. The palate proper,* ,"; · e., tl1 e m· t er-ml olar portion, is extremely contracted· its widt·h ante n·o r1 Y b C·i ng no greater t mn that of one of the molars. It widens a little backward It . d 1 · f . Is eep y twtce urrowed, having a strong median ridge separating the furrows and strong alveolar ridges on either hand. Posteriorly th . . f 'd 't t d' ' ere IS a pair o eep JH·d s ex en mg to opposite the penultimate molars , and d'lV .l u..~ ec I •o· y a s t rong r~ ge. The palatal plate upon which these pits are constructed reaches con-siderably back of the molars in Geomys . less so in ,.,L~-·· - Th bl ' .L ,w,umtys. e general resem ance of the parts to some A . r . tl . . . rvu:v tnm IS strong. The ptery(J'oids are udn, bvertl.cal, an~ somew~at circular plates, divaricating a little po:teriorly an a uttmg agamst the ttps of the b ll T ' tion of th d' . . u a osscn hey appear like a bifurca-e me . tan palatal ndge Just mentioned Th being contracted, like the palate itself. and , . d . e post-palatal parts not e~sy ~o fully appreciate the confor:natio~o;p:::s;ar~:lto ~l~~.~~s~ace, it is descrtbe tt. Moreover, the lamellar t . 'd ' an s I ess so to •, p et ygm s are often broken off in care- Ibe long upward-sloping anterior a ~ f . outside tbe mouth, like tbo snperior . . P r .. o palate 18 uot "palate " at all. Iu life, it is nltogethor IUCJsors, and covered with furry skin. COUES ON GEOMYS AND THOMOMYS-OSTEOLOGY. 271 less preparation of the skull, and in such a way that scarcely a suggestion of their former presence is left. Behind the pterygoids, the conspicuous bullre ossre appear convergent anteriorly to touch the former, prolonged into a tube exteriorly. Between them, the basi-occipital space is cuneiform (especially in Thorrwmys-more nearly quadrangular in Geomys), with a median ridge and lateral depressions, nicked behind by a small portion of the foramen magnum. The skull finishes behind by an irregular curve, substantially the same as that described in speaking of the occipital plane. In all but the oldest animals, the following sutures, or, at any rate, traces of them, persist: internasal, nasa-intermaxillary, maxillo-intermuxillary, frontonasal, fronto-intermaxillary, and fronto-maxillary ; maxillo-malar, squamaparietal. squamo-malar, squamo-mastoid, occipito-mastoid, occipito-petrosal; basi-occipito-sphenoid; ~nd there is fissured separation of the petrosal and tympanic from the squamosal. The various intricate relations of the palatals, and of the ''sphenoid" as a whole, are inappreciable in the adult skull. Detailed relations of such of the individual bones as can be made out from the material before me here follow : The nasals reach back 1o a point opposite the anterior root of the zygoma, but extend little, if any, in the other direction, beyond th~ intermaxillaries. For two-thirds their extent they are narrow and approxtmutely parallel in the examples of Geomy.o; before me, and then rapidly expand. ~n · all the Thomomys I have seen, they widen regularly from the base to tip. The are flat at first, but toward the end become somewhat volute or scroll-like. y They remain permanently distinct from the m· termax1· na n·e s, an d ha ve failed in no case to show me separation from each other. The intermaxillaries run up on the forehead farther than the nasals-to or beyond the back instead of front border of the zygomata. being received in a deep ernargination of the frontal. Below, similarly, t~ey. r.un far d~wn on the false palate, ending opposite the buck end.of ~he mcts~ve foramma. Their course arouncl the side of the rostrum (maxlllo-mtermaxtllary suture) may usually be traced as a strongly convex curve between the upper ~nd lower points just mentione(l, the most forward port.ion of the cu:ve lymg nearly midway between zygoma and incisor~. The lateral surface IS thrown into a curved elevation, d eno tw. g th e t. rae<l o f the incisor wit.hin. A strong |