OSTEOLOGY OF THE HORSE. 43 



the occipital hole. 2d, On either side, in the same direction, the 

 internal surface of the tving of the ethmoid bone, rather more con- 

 vex than concave, for the support of the anterior lobe of the cere- 

 brum ; the concavity oj the wing of the sphenoid bone, for the re- 

 ception of the middle lobe ; the concavity of the squamous part of 

 the temporal bone, for lodging the posterior lobe : and the sutures 

 bounding these three cerebral surfaces. The foramen lacerum 

 basis cranii, formed between the wing of the sphenoid anteriorly, 

 the basilar process of the occipital bone internally, and the petrous 

 portion of the temporal bone externally and posteriorly : it is wide 

 and irregular before, narrow behind, and is distinguished into 

 the spheno-occipilal and temporo-occipital hiatus. — Th e petrous 

 PORTION OF THE TEMPORAL BONE, presenting a narrow tri- 

 angular surface forwards and upwards, which contributes to the 

 posterior cerebral concavity ; a broad smooth but uneven surface 

 inwards, against which inclines the cerebellum, and upon which 

 we distinguish — a, the orifice of the meatus auditorius internus ; 

 bf a transverse prominence, and several cerebral indentations ; 

 c, an irregular convexity downwards, which forms the boundary 

 wall of the labyrinth ; d, ?i fissure separating it from the former. 

 Lastly, the sutures, uniting the petrous to the squamous portion 

 and to the occipital bone. — Of the occipital bone, a part of 

 the internal surface assisting in the formation of a concavity for 

 the cerebellum, by the convolutions of which it is indented ; the 

 surface even and smooth, and slightly excavated below this, for 

 the support of the medulla oblongata ; still lower, the condyloid 

 foramina, through which the ninth pair of nerves pass out. 



11.— THE ORBITS, 



Two in number, are formed for the lodgement, attachment, 

 and protection of the eyes and their appendages. 



Figure. — Symmetrical. The cavity, which is extended hori- 

 zontally backward and inward, has, viewed in front, a pyramidal 

 aspect : the base, represented by the front, has four sides and 

 four angles ; one only of the sides, however, is sulEficient in extent 

 to reach the apex, the others being all more or less imperfect. 

 A line drawn in the horizontal direction through the axis of this 

 figure, inclines more outwards than forwards, more forwards than 

 downwards, intersecting another horizontal line projected directly 

 forward at an angle of about 70", and one extended laterally, di- 

 rectly outward, (at right angles with the former) at about 20°: 

 Ihe inclination downward, liowever, will in course vary with the 

 erect position of the head. 



Structure. — The orbit is composed of unequal portions coming 



