46 



THE BONES. 



Fig. 21. 



opens into the incisive foramen. These three faces are separated by as 

 many borders : tico internal, limiting before and behind the corresponding 

 face ; and an external, separating the labial from the buccal face. The latter 

 only merits notice ; it is very thick, and is divided into two parts : an 

 inferior, which describes a curved line with the concavity upwards, and 

 is hollowed by three alveoli to receive the incisor teeth ; another, the 

 superior, is straight, vertical, and somewhat sharp, and forms a part of 

 the dental interspace. It is limited above, near the base of the external 

 process, by a cavity for the formation of the alveolus of the tusk. 



Processes. These are distinguished as ex- 

 ternal and internal. The first, the longest and 

 strongest, is flattened on both sides ; its ex- 

 ternal face is smooth and continued with that 

 of the thick portion of the bone ; its internal 

 face is covered by the mucous membrane of 

 the nose ; the anterior border is smooth and 

 rounded; the posterior, denticulated to re- 

 spond to the supermaxillary bone, is in con- 

 tact with the external border of the base ; its 

 summit is thin, and is insinuated between the 

 latter and the nasal bone. The internal pro- 

 cess, the smallest, is flattened from before to 

 behind, and forms a very thin tongue of bone, 

 separated from the other portions by a nar- 

 row and very deep notch named the incisive 

 opening or cleft. Its inferior face constitutes a 

 small portion of the floor of the nasal fossae ; 

 the posterior, continuous with the same face 

 of the principal mass of the bone, forms part 

 of the palatine roof; its external border cir- 

 cumscribes, inwardly, the incisive opening ; 

 the internal is united by dentated suture with 

 the opposite bone. 



Structure and development. It is a spongy 

 bone, developed from a single nucleus. 



3. Palate Bones. 



Ike palate bones are situated between the 

 supermaxillaries, at the margin of the guttural 

 opening of the nasal cavities, and are articu- 

 lated with the sphenoid, ethmoid, vomer, 

 frontal, and pterygoid bones. Elongated from 

 above to below, flattened laterally, and curved 

 Foramen magnum ; 3, 3, Oc- 

 cipital condyles; 4, 4, Styloid processes; 5, 5, Petrous bone; 6, Basilar process; 7, 

 Pterygoid fissure of the sphenoid bone ; 8, Foramen lacerum ; 9, 9, Supra-condyloid, or 

 anterior mastoid process; 10, 10, Articular eminence, or temporal condyle; 11, 'Body ot 

 sphenoid bone; 12, Pterygoid process; 13, Ethmoid bone; 14, Temporal bone and sphe- 

 noidal suture; 15, Lachrymal bone; 16, Vomer; 17, Malar bone; 18, Maxillary tube- 

 rositvj 19, Posterior, or guttural opening of the nose; 20, Palate bone; 21, Palatine 

 styloid process ; 22, Palato-maxillary foramen ; 23, Palatine process of superior maxil- 

 lary bone with suture ; 24, Ditto of premaxillary bone ; 25, Premaxillary bone ; 26, 

 Upper incisor teeth ; 27, Point of junction of the premaxillary with the superior maxil- 

 lary bone ; 28, Upper molar teeth young mouth. 



POSTERIOR ASPECT OF HORSE'S 

 SKULL. 



1, Occipital protuberance ; 2, 



