62 the skeleton of the horse 



The Malar Bones 



The malar or zygomatic bones (Ossa zygomatica) are placed between the lac- 

 rimal above and the maxilla below and in front. Each is irregularly triangular in 

 outline and presents three surfaces, three borders, a base, and an apex. 



The facial surface is smooth, slightly convex, wide in front, and narrow behind. 

 At its lower part it presents the facial or zygomatic crest, which is continuous 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 separated from the facial surface by the concave orbital 

 margin. It is concave and smooth, and forms part of the lower and front wall of 

 the orl)it. 



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 superior border articulates with the lacrimal chiefly, but to a small extent 

 behind with the maxilla also. 



The inferior border and the base articulate with the maxilla. 



The apex 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 Turbinal 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, cribriform 

 in many places, and covered on both sides with mucous membrane in the fresh 

 state. They are arranged in two pairs, superior and inferior. 



The superior or naso-turbinal (Concha dorsalis)^ is somewhat cylindrical in 

 form, small at its anterior part, and flattened transversely. It is attached to the tur- 

 binal crest of the nasal bone and the nasal plate of the frontal bone. The anterior 

 part is rolled like a scroll one and a half times, thus inclosing a cavity which com- 

 municates with the middle meatus nasi. The arrangement is best seen on a cross- 

 section (Fig. 37) . The posterior part is not rolled, but its lower border is attached to 

 the lateral nasal wall, thus helping to inclose a large space which is part of the fron- 

 tal sinus. This cavity is separated from that of the scroll-like part by a transverse 

 septum. The internal surface is flattened, and is separated from the septum nasi 

 by a narrow interval, the common meatus (Meatus nasi communis). Another 

 narrow passage, the superior meatus (Meatus nasi superior), separates the upper 

 surface from the roof of the nasal cavity. The space between the lower surface 

 and the inferior turbinal is the middle meatus (Meatus nasi medius). The anterior 

 extremity is prolonged toward the nostril by two small bars of cartilage. 



The inferior or maxillo-turbinal bone (Concha ventralis) is shorter and smaller 

 posteriorly than the upper one. It is attached to the inferior turbinal crest, and 

 consists, like the upper one, of an anterior coiled and a posterior uncoiled portion. 



To express briefly the mode of coiling of the two bones of the same side we may say that 

 they are rolled toward the septum and eacli other. 



The inferior and posterior borders of the posterior part are attached to the 

 maxilla, thus helping to inclose a cavity which is part of the maxillary sinus. The 

 lower surface is separated from the floor of the nasal cavity by the inferior meatus 

 (Meatus nasi inferior), which is much larger than the other nasal passages. The 

 anterior extremity is prolonged to the nostril by a curved bar of cartilage. 



Development. — Each ossifies in cartilage from a single center. 

 ' This bone is really a greatly developed first ethmo-turbinal. 



