20 ANATOMY OF THE HORSE. 



posteriorly, of the occipital ; laterally, of the four temporals ; 

 inferiorly and anteriorly, of the ethmoid ; inferiorly and in the 

 middle, of the sphenoid ; inferiorly and posteriorly, of the occipi- 

 tal bone. 



FRONTAL BONES. (OSSA FRONTIS.) 



Situation. The frontal bones form the antero-superior part of 

 the cranium, that broad flat part which we term the forehead, 

 and which in the living horse is commonly marked with a patch 

 of white hair, denominated a star. 



Figure — Irregular. Flat, superiorly; concave, underneath. 



Division — Into two surfaces and four borders. 



T/ie External Surface is flat and smooth, sometimes even 

 slightly depressed in the situation of the frontal sinus. Pro- 

 jecting from it outwardly is the external orbital process, forming 

 the frontal arch and articulating with the temporal bone : un- 

 derneath, the arch is excavated for the reception of the lachry- 

 mal gland ; and through its inward end is a hole, (in some rare 

 nistances, two,) the supra-orbital foramen, for the transmission 

 of a small artery and nerve of the same name to the forehead ; 

 below the foramen, internally, is a small depression, marking the 

 place of attachment of the cartilaginous pulley belonging to the 

 superior oblique muscle of the eye. From below and behind 

 the arch proceeds downwards and backwards the internal orbi- 

 tal process or plate, divided into two by a notch into which pro- 

 jects the wing of the ethmoid bone, whose extremity is received 

 into a mortise formed within the base of this plate ; this part 

 also articulates, within the orbit, inferiorly, with the sphenoid, 

 posteriorly, with the temporal, and, anteriorly, with the lachrymal 

 and superior maxillary bones. The anterior portion of this pro- 

 cess, behind, where it joins the sphenoid, is pierced by the in- 

 ternal orbital foramen, which gives passage to the lateral nasal 

 nerve ; the surface behind the posterior portion is smooth and 

 depressed, making by union with it part of the temporal 



The Internal Surface is divided by a vaulted cranial septum 

 into two unequal concavities: the posterior forms a cap for the 

 anterior lobe of the cerebrum, which rests upon the septum, the 

 indentations upon the surface answering to the cerebral emi- 

 nences ; the anterior concavity constitutes the frontal sinus, 

 whose interior is much enlarged by the slant taken by the septum, 

 and the cavity continues to extend with age until it occupies the 

 entire front of the bone. One frontal sinus is separated from the 

 other by the nasal spine, composed of a lamina from each 



