XIII 



PHYLUM CHORDATA 



523 



the junction of the supra-occipital and parietals ; but the temporal 

 ridges do not meet in the middle to form a sagittal crest such as 

 occurs in the skull of the Horse. There are prominent paroccipital 

 processes. There is a large, but compressed, bulla tympani ; the 

 auditory meatus is very long, directed upwards and outwards, and 

 is surrounded by the post-glenoidal and post-tympanic processes, 

 which are in contact with one another. The mastoid is rudi- 

 mentary, and does not appear on the outer surface of the skull. 

 The frontal develops a short post-orbital process ; but this does 



Pa. 



Fio. 1167. Section of skull of Sheep (Ovis aries). AS, alisphenoid ; bh. basi-hyal ; B3. 

 basi-occipital ; BS. bast-sphenoid ; cd. condyle ; ch. cerato-hyal ; cp. coronoid process ; eh. 

 epihyal ; EO. ex-occipital ; ET. ethmo-turbiual ; Fr. frontal ; ME. mesethmoid ; MT. 

 maxillary turbinal ; MX. maxilla ; Na. nasal ; OS. orbito-sphenoid ; Pa. parietal ; PL 

 palatine ; Per. periotic ; P. MX. pre-maxilla ; P.S. pre-sphenoid ; PI. pterygoid ; s.h. 

 stylo-hyal ; SO. supra-occipital (with inter-parietal) ; pp. par-occipital process ; th. thyro- 

 hyal ; Ty. tympanic ; Vo, vomer. (After Flower.) 



not meet the zygoma, so that the bony margin of the orbit is 

 incomplete behind. The facial region as a whole is elongated and 

 laterally compressed. The nasals are long and narrow, and the 

 premaxillse send backwards long processes on each side of them. 

 A peculiar bone the pre-nasal is developed in the nasal septum. 

 The condyle of the mandible is transversely elongated ; the coronoid 

 process very small. 



The skull of the Hippopotamus differs from that of the Pig 

 mainly in the proportions of the various parts. The cranial cavity 

 is relatively small, and the face large. The orbits are almost 



