70 THE SKELETON OF THE HORSE 
THE VOMER 
The vomer is a median bone, which assists in forming the ventral part of the 
septum nasi. It is composed of a thin lamina which is bent (except in its posterior 
part) so as to form a narrow groove (Sulcus vomeris), in which the lower part of the 
perpendicular plate of the ethmoid bone and the septal cartilage are received. The 
lateral surfaces, right and left, are highest near the posterior end and diminish 
gradually to the anterior end; they are slightly convex dorso-ventrally, and are 
covered by the nasal mucous membrane during life. The ventral border is thin 
and free in its posterior third, and divides the choane or posterior nares medi- 
ally; in the remainder of its extent it is wider and is attached to the nasal crest. 
The anterior extremity lies above the ends of the palatine processes of the premax- 
ille. The posterior extremity consists of two wings (Ale vomeris) which extend 
outward below the body of the presphenoid; posteriorly they form a notch (In- 
cisura vomeris), and laterally join the palatine and pterygoid bones. 
Development.—The vomer is primitively double, and ossifies from a center on 
either side in the membrane covering the cartilaginous septum nasi; the two 
laminze then fuse below and form a groove. 
THE MANDIBLE 
The mandible (Mandibula),' or lower jaw bone, is the largest bone of the 
face. The two halves of which it consists at birth unite during the second or third 
month, and it is usually described as a single bone. It carries the lower teeth, and 
articulates by its condyles with the squamous temporal on either side. It consists 
of a body and two rami.” 
The body (Corpus mandibul) is the thick anterior part which bears the incisor 
teeth. It presents two surfaces and a border. The lingual surface (Facies lin- 
gualis) is smooth and slightly concave; during life it is covered by mucous mem- 
brane, and the tip of the tongue overlies it. The mental surface (Iacies mentalis) 
is convex and is related to the lower lip. It is marked by a median furrow which 
indicates the position of the primitive symphysis mandibule. The curved alveolar 
border (Limbus alveolaris) presents six alveoli for the incisor teeth, and a little 
further back two alveoli for the canine teeth in the male; in the mare the latter are 
usually absent or small. 
The rami (Rami mandibule) extend backward from the body and diverge to 
inclose the mandibular (or submaxillary) space (Spatium mandibulare). Each 
ramus is bent so as to consist of a horizontal part (Pars molaris) which bears the 
lower cheek teeth, and a vertical part (Ramus mandibule [S. N. A.]) which is ex- 
panded and furnishes attachment to powerful muscles; the term angle is applied 
to the most prominent part of the curve. The ramus presents two surfaces, two 
borders, and two extremities. The lateral surface is smooth and slightly convex 
from edge to edge on the horizontal part; at the junction with the body it presents 
the mental foramen (Foramen mentale), which is the external opening of the man- 
dibular canal. On the vertical part it is somewhat concave and presents a number 
of rough lines for the attachment of the masseter muscle. The medial surface of 
the horizontal part is smooth, and presents a shallow longitudinal depression in its 
middle; above this there is often a faint mylo-hyoid line (Linea mylohyoidea) for 
the attachment of the muscle of like name. At the lower part of the junction with 
the body there is a small fossa for the attachment of the genio-hyoid and genio- 
1 This bone is also commonly called the inferior maxilla. 
2 In the Stuttgart Anatomical Nomenclature (S. N. A.) the body (Corpus) is the part which 
bears the teeth, and is divided into a pars incisiva and a pars molaris. The ramus is the rest of 
the bone. This mode of description is copied from the Basel Nomina Anatomica. It does not 
seem to the author to be well adapted to comparative purposes. 
