262 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



Comparison of the auditory region in the skull of 

 these seven divergent Eocene species shows that the 

 auditory meatus tends to close in the brachycephalic 

 types, is moderately open in the mesaticephahc types, 

 and is widely open in the dolichocephalic types of 

 titanotheres, and thus parallels the auditory region of 

 some modern perissodactyls, as shown in Figure 379. 



The chief aUometric characters that distinguish the 

 Eocene titanotheres are the following: 



1. Abbreviation of the face (brachyopy) and elongation of the 

 cranium (dolichocrany), combined with general brachycephaly 

 or with general doliohooephaly. 



2. Flexure of the face upon the cranium ( = cyptocephaly, 

 upward or downward bending). 



3. Broadening and elongating of the nasals or narrowing and 

 recession of the anterior narial openings. 



4. Pneumaticity, development of great pneumatic cavities in 

 the upper part of the face and cranium. 



We observe a long series of modifications of all the 

 great adaptive functions in the evolution of the 

 mammalian skull — namely, (1) prehension of food, 

 (2) mastication of food, (3) passage of food to the 

 fauces, (4) channels of respiration, (5) lodgment of 

 sense organs, (6) lodgment of the brain, (7) offensive 

 use of the canine teeth, (8) offensive use of the horns. 

 It would appear that the two functions last indicated 

 (7, 8) exert little influence in the middle Eocene 

 titanotheres. In wide contrast are the latest Eocene 

 and the Oligocene titanotheres, in which the horns 

 predominate. The canines vary greatly in size and in 

 the telmatheres become effective offensive weapons. 

 The prehensile functions of the lips and anterior teeth 

 vary with the development of a broad muzzle, the 

 firmly united premaxUlae, the greater or less recession 

 of the nasal bones ; but there is little evidence of strong 

 development of prehensile powers in the upper lip such 

 as is seen in the skull of the tapirs. 



nST OF ABBREVIATIONS USED IN ILLUSTRATIONS 

 OF SKULLS 



The following abbreviations are used in this mono- 

 graph in the illustrations of skulls. Names of com- 

 plete bones are begun with capital letters; names of 

 parts of bones with small letters. 



As. Alisphenoideum. 



Bo. Basioccipitale. 



Bs. Basisphenoideum. 



c. As (car. ex. mx.). canalis alisphenoideus, carotis externa, 



ramus maxiUaris. 

 c. i. o. (V2 car. ex.). canalis infraorbitalis, nervus maxillaris, 



carotis externa, 

 cond. ac. condylus occipitalis accessorius. 

 cond. condylus occipitalis, 

 cr. lamb, crista lambdoidea. 

 cr. sag. crista sagittalis. 

 or. tem. crista temporalis, 

 dct. la. ductus nasolacrymalis. 

 em. ar. eminentia articularis. 

 em. Fr. eminentia frontalis. 

 Ex. o. Os exoccipitale. 

 f. 0. (XII). foramen condylare, nervus XII. 



f. la. foramen lacrimale. 



f. 1. a. (Ill, IV, V, VI). foramen lacerum anterius, nervi III, 



IV, V, VI. 

 f. 1. m. (car. in.), foramen lacerum medium, carotis interna, 

 f. 1. p. (IX, X, XI). foramen lacerum posterius, nervi IX, 



X, XI. 

 f. mg. foramen magnum, 

 f. mn. (V3). foramen mentale, nervus V3. 

 f. ms. (jug.), foramen mastoideum. 

 f. op. (II). foramen opticum, nervus II. 

 f. ov. (V3). foramen ovale, nervus V3. 

 f. pi. a. (N. nas. pi.), foramen palatinum anterius, nervus 



nasopalatinus. 

 f. p. gl. foramen postglenoideum. 

 f. pi. p. (N. pi. post.), foramen palatinum posterius, nervus 



palatinus posterior, 

 f. r. (V2). foramen rotundum, nervus Vj. 

 f. sph. pi. (V2). foramen sphenopalatinum. 

 f. stm. (VII). foramen stylomastoideum, nervus VII. 

 f. su. or. foramen supraorbitale. 

 f. ven. foramen venosum. 

 fis. nar. ant. fissura narialis anterior, 

 fos. gl. fossa glenoidea. 

 fos. interpa. fossa interparietale. 

 fos. men. in. fossa menisci interna, 

 fos. nar. ant. fossa narialis anterior, 

 fos. nar. post, fossa narialis posterior, 

 fos. st. hy. fossa ossis stylohyoidei. 

 Fr. Os frontale. 

 HI Umbo cornu ("horn"). 

 I. P. Os interparietale. 



La. Os lacrimale. 



lig. nu. ligamentum nuchae. 



m. a. e. meatus acusticus externus. 



m. obi. cap. sup. musculus obliquus capitis' 

 superior. 



m. rect. cap. lat. musculus rectus capitis later- 

 alis. 



m. rect. cap. post, musculus rectus capitis 

 posticus. 



Ms. mastoideum. 



ms. Per. pars mastoidea, ossis periotici. 



Mx. maxiUa. 



Mx. (alv.) maxilla (processus alveolaris). 



Mx. tb. maxilloturbinale. 



Na. Os nasalis. 



nar. post, naris posterior. 



obi. cap. sup. musculus obliquus capitis superior. 



Orb. Orbis. 



Pa. Os parietale. 



petr. pars petrosa ossis periotici. 



p. gl. Sq. Processus postglenoideus ossis squamosi. 



PL Os palatinum. 



Pmx. Premaxilla. 



p. o. Ex. Processus paroecipitalis ossis exoccipitalis. 



p. o. Fr. Processus postorbitalis ossis frontalis. 



p. o. Mai. Processus postorbitalis ossis malaris. 



pr. cor. processus coronoideus. 



pr. i. o. Mai. processus infraorbitalis ossis malaris. 



pr. p. o. processus postorbitalis. 



Psph. Os presphenoideum. 



Pt. Os pterygoideum. 



pt. As. Processus pterygoideum ossis alisphenoidei. 



p. ty. Sq. processus post-tympanicus ossis squamosi. 



rect. cap. musculus rectus capitis (antice) . 



rect. cap. post, musculus rectus capitis posticus. 



sin. lat. eth. sinus lateralis ethmoidalis. 



So. Os supraoccipitale. 



Sq. Os squamosum. 



(attachments). 



