68 THE SKELETON OF THE HORSE 
Development.—Each nasal bone ossifies in membrane from a single center, 
The nasal suture does not close completely even in old age. In some cases the two 
plates separate to inclose a small air-space (nasal sinus) in the posterior part. 
THE LACRIMAL BONES 
The lacrimal bones (Ossa lacrimalia) are situated at the anterior part of the 
orbit, and extend forward on the face to the posterior border of the maxilla. Each 
presents three surfaces and a circumference. 
The lateral face is clearly divided into orbital and facial parts by the orbital 
margin. The orbital surface (Facies orbitalis) is triangular in outline, smooth and 
concave; it forms part of the medial and front wall of the orbit. Near the orbital 
margin it presents a funnel-like fossa (I’ossa sacci lacrimalis), which is the entrance 
to the lacrimal canal; the fossa is occupied by the lacrimal sac, which is the dilated 
origin of the naso-lacrimal duct. Behind this is a depression in which the inferior 
oblique muscle of the eye takes origin. The facial surface (Facies facialis) is more 
extensive, and has the form of an irregular pentagon. It is slightly convex and 
smooth in the foal, flattened in the adult. It usually bears the small lacrimal 
tubercle, which is situated nearly an inch (ca. 2 em.) from the orbital margin. 
The orbital margin (Margo orbitalis) is concave, rough above, smooth below. 
The nasal surface (Facies nasalis) faces into the frontal and maxillary sinuses. 
It is concave and very irregular, and is crossed almost horizontally by the osseous 
lacrimal canal (Canalis lacrimalis osseus). 
The circumference articulates dorsally with the frontal and nasal bones, 
ventrally with the malar and maxilla, in front with the maxilla, and behind with 
the frontal. The various sutures so formed are designated by combinations of the 
names of the bones. 
Development. 
Each ossifies in membrane from a single center. 
THE MALAR BONES 
The malar or zygomatic bones (Ossa zygomatica) are placed between the lae- 
rimal above and the maxilla below and in front. Each is irregularly triangular in 
outline and presents three surfaces, three borders, and a process. 
The facial surface (Facies facialis) is smooth, shghtly convex, wide in front, 
and narrow behind. At its lower part it presents the facial crest, which is continu- 
ous in front with the similar ridge on the maxilla and behind with the zygomatic 
process of the temporal; the crest is rough below, where the masseter muscle is 
attached to it. 
The orbital surface is much smaller than the facial surface, from which it is 
separated by the concave orbital margin (Margo orbitalis). It is concave and 
smooth, and forms part of the lower and front wall of the orbit. 
The nasal surface is concave and faces into the maxillary sinus. In the young 
foal a considerable part of it articulates with the maxilla. 
The dorsal border articulates with the lacrimal chiefly, but to a small extent 
behind with the maxilla also. 
The ventral and anterior borders articulate with the maxilla. 
The posterior extremity is formed by the zygomatic process, which is beveled | 
above and is overlapped by the zygomatic process of the temporal bone. 
Development.—Each ossifies in membrane from one or two centers. } 
THE TURBINATE BONES 
These (Ossa turbinata) are delicate, scroll-like bones, four in number, which | 
are attached to the lateral walls of the nasal cavity. They project into the cavity | 
and greatly diminish its extent. Each is composed of a very thin lamina, cribri- 
