68 THE SKELETON OF THE HORSE 



mits vessels and nerves of like name to the nasal cavity. The lower foramen, the 

 posterior palatine, transmits the palatine artery and nerve to the palatine canal. 

 The upper part of the fossa is smooth, and is crossed by the internal maxillary 

 artery and the maxillary nerve. The lower part is chiefly roughened for the attach- 

 ment of the internal pterygoid muscle, but is crossed in front by a smooth groove 

 in which the palatine vein lies. 



The maxillary or preorbital region is formed chiefly by the maxilla, but also by 

 the premaxilla, and the facial parts of the lacrimal and malar bones. Its contour 

 is approximately triangular, the base being posterior. It offers two principal 

 features. The facial crest extends forward from the lower margin of the orbit, 

 and ends abruptly at a point about an inch and a half (3 to 4 cm.) above the third 

 or fourth cheek tooth ;^ its inferior aspect is rough for the attachment of the masse- 

 ter muscle. The infraorbital foramen is situated in a transverse plane about an 

 inch (ca. 2 to 3 cm.) in front of the end of the crest and about two inches (5 cm.) 

 above it. The foramen opens forward, and through it the infraorbital artery and 

 nerve emerge. The surface over the premolar teeth varies greatly with age, in 

 conformity with the size of the embedded parts of the teeth. In the young horse 

 the surface here is strongly convex, the outer plate of bone is thin and even defective 

 sometimes in places, and the form of the teeth is indicated by eminences (Juga 

 alveolaria). In the old animal the surface is concave on account of the extrusion 

 of the teeth from the bone. The downward curve of the premaxilla is pronounced 

 in the young subject, very slight in the aged. 



The inferior or basal surface (Norma basalis), exclusive of the mandible, 

 consists of cranial, guttural, and palatine regions. 



The cranial region (Basis cranii externa) extends forward to the vomer and 

 pterygoid processes (Fig. 28) . At its posterior end is the foramen magnum, flanked 

 by the occipital condyles. External to the latter is the condyloid fossa, in which 

 is the h5rpoglossal foramen, which transmits the hypoglossal nerve and the con- 

 dyloid artery and vein. Further outward are the paramastoid or styloid proc- 

 esses (Processus jugulares) of the occipital bone. Extending forward centrally is 

 a prismatic bar, formed by the basilar part of the occipital and the body of the 

 sphenoid bone; at the junction of these parts are tubercles for the attach- 

 ment of the ventral straight muscles of the head. On either side of the basilar 

 part of the occipital is the foramen lacerum basis cranii, bounded externally by 

 the base of the petrous temporal bone. In front of these the region becomes very 

 wide on account of the lateral extension of the zygomatic processes, bearing on the 

 ventral aspect the condyle and glenoid cavity for articulation with the mandible. 

 Beyond this the process turns forward and joins the zygomatic process of the malar, 

 completing the zygomatic arch and the surface for the attachment of the masseter 

 muscle. On either side of the body of the sphenoid is the infratemporal fossa, 

 formed by the temporal wing and the root of the pterygoid process of the sphenoid 

 bone. It is bounded in front by the pterygoid crest, which separates it from the 

 orbit and the pterygo-palatine fossa. In it is the pterygoid or alar foramen, which 

 transmits the internal maxillary artery. A little lower is the entrance to the ptery- 

 goid (Vidian) canal. 



The guttural region presents the pharyngeal orifice of the nasal cavity. This is 

 elliptical and is divided in its depth medially by the vomer into two posterior 

 nares or choanae. It is bounded in front and laterally by the palate and pterygoid 

 bones, behind by the vomer. It is flanked by the hamular process of the pterygoid 

 bones. The plane of the opening is nearly horizontal, and the length is about 

 twice the width. 



The palatine region comprises a little more than half of the entire length 



' This relation varies with age; in the young horse the third tooth, in the old subject the 

 fourth, lies below the end of the crest. 



