527 



3136. The skull of a Horse (Equus Caballus). 



The maxillo-premaxillary sutures are obliterated. 



3137. The skull of a Mare (Equus Caballus). 



Hunterian. 



This is characterized by the rudimental state of the canines, of which that of the right side, 

 upper jaw, is shed, and the socket almost obliterated. If the equine skull be compared with 

 that of the Rhinoceros, the basioccipital will be seen to be narrower and more convex, the 

 rides, in some (Nos. 3133 and 3135, e.g.), being separated by an angle from the under sur- 

 face. The true mastoid intervenes, as a tuberous process, between the post-tympanic and 

 paroccipital processes, clearly indicating the true nature of the post-tympanic in the Rhino- 

 ceros ; the Tapir shows an intermediate condition of the mastoid between the Rhinoceros and 

 Horse. The latter differs from both the Tapir and Rhinoceros in the outward production of 

 the sharp roof of the orbit and the completion of the bony frame of that cavity behind by the 

 junction of the postorbital process with the zygoma. The temporal fossa, so defined, is small 

 in proportion to the length of the skull : the base of the postorbital process is perforated by 

 a superorbital foramen : the lacrymal canal begins by a single foramen. The premaxillaries 

 extend to the nasals, and shut out the maxillaries from the anterior aperture of the nostrils. 

 The chief marks of affinity to other Perissodactyles are seen in the shape, size and formation 

 of the posterior aperture of the nostrils, the major part of which is bounded by the palatine 

 bones, of which only a small portion enters into the formation of the bony palate, which ter- 

 minates behind opposite the interspace between the penultimate and last molars. A narrow 

 groove divides the palato-pterygoid process from the socket of the last molar, as in the Tapir 

 and Rhinoceros. The pterygoid process has but little anterc-posterior extent : its base is per- 

 forated by the ectocarotid canal. The entopterygoids are thin plates applied like splints over 

 the inner side of the squamous suture between the pterygoid processes of the palatines and 

 alisphenoids. The postglenoid process is less developed than in the Tapir. The eustachian 

 process is long and styliform. There is an anterior condyloid foramen, and a wide ' fissure 

 lacera.' The broad and convex bases of the nasals articulate with the frontals a little behind 

 the anterior boundary of the orbits v The space between the incisors and molars is of greater 

 extent than in the Tapir : a long diastema is not, however, peculiar to the Horse, and, although 

 it allows the application of the bit, that application depends rather upon the general nature of 

 the Horse, and its consequent susceptibility to be broken in, than upon a particular structure 

 which it possesses in common with the Ruminants and some other Herbivora. 



Hunterian. 



3138. The skull of a Mare (Equus Caballus). Presented by Henry Cline, Esq. 



3139. The skull, vertically and longitudinally bisected, of a Horse (Equus Caballus). 



The air-cells do not extend further back than the fore part of the frontals above the cra- 

 nial cavity, and of the basisphenoid beneath. Ossification extends into the base of the ten- 



