SKULL MAMMALS 



217 



give off in front a pair of long processes which meet in the middle line. Laterally 

 the basihyal is continued in a broad cartilage thyreohyal. Possibly a stylohyal 

 connects with the mastoid. 



Embrythopoda (Barypoda).— The cranium, much Uke that of Htyracoids 

 in premaxilla, lacrimal, nasal and frontal, has the sutures largely obliterated, 

 a strong lambdoid crest, moderate zygoma, and orbit and temporal fossa con- 

 tinuous. The supraoccipital, excluded from the foramen magnum, incUnes 

 forwards, the parietal region is nearly flat, the frontals have small horn cores, 

 larger ones are on the nasals. Lacrimal and nasal are fused, a single incisive 

 foramen occurs, and the orbit is bounded below entirely by the zygomatic bone 

 which extends to the mandibular fossa. The palatines extend laterally far 

 behind the choanae. There is an alisphenoidal canal. Paroccipital and post- 

 tympanic processes are close together, the latter bounding the auditory meatus 

 behind. Pre- and postglenoid processes are present. The halves of the lower 

 jaw are fused in a long symphysis, the coronoid process is high, the condylar, 

 with a rounded condyle, is slight. 



Proboscidia.— The skulls of elephants and their aUies are larger because 

 of extensive pneumatization, there being numerous spaces in the cranial walls 



I 



(fig. 229), the cavities extending 

 into several of the facial bones. 

 The history of the order, now 

 pretty well known, shows an 

 increase in skull size to accommo- 

 date the incisors (tusks) and 

 molars which are very large in 

 recent species. This increase is 

 seen especially in the premaxillae, 

 the great size of which and the 

 development of the trunk, carries 

 the nares back so that the nasal 

 canals and the mesethmoid are 

 nearly vertical, the nasal bones 

 being reduced. Except in Dino- 

 therium, orbit and temporal fossa 

 are partly separated by postorbital processes. The zygoma is slender, the 

 zygomatic bone forming its middle part. 



The supraoccipital separates the parietals behind, it and the parietals forming 

 most of the roof of the cranial cavity, the latter reaching down in the side walls 

 to the squamosals, these parts separating squamosals and supraoccipital. The 

 frontals roof the orbits; the lacrimal, perforate or entire, is small and sometimes 

 is fused with the adjacent bones. Tympanic and petrosal fuse early, both 

 forming the bulla. A postglenoid process is absent, and the posttympanic hmits 

 the circular mandibular fossa behind and encloses the auditory meatus. The 

 halves of the lower jaw are fused at the symphysis, the ramus is high, the condyle 

 rounded and the alveolar part of the jaw is large. The condylar processis 

 usually lower than the coronoid. 



Fig. 229. — Section of cranium of elephant 

 (Zittel, '93). b, brain-case; c, condyle; e, eth- 

 moid;/, frontal; i, incisor (tusk); m, maxilla; n, 

 naris; p, parietal; pm, prema.xilla; 5, supraocci- 

 pital; 1,2, molars. 



