ANTERIOR ARCH AND LIMB. 291 



The central part of the facial area is formed by two nasal 

 bones (N and Na), flat bones of an elongated triangular form 

 extending down the nasal cavities. Placed on each side of 

 these central ones are the supra-maxiUary bones (SIH), which 

 carry teeth. In front come the two other tooth-bearing bones, 

 the premaxillaries {P.Mx and PM). In the nasal tubes are two 

 spongy structures, the turbinated bones (Turb) ; and between the 

 facial and cranial portion comes the ethmoid, which is perforated 

 in one part, forming the cribriform plate, situated at the end 

 of the nasal fossae. The floor of the facial area (or the roof of 

 the mouth) is built up of vomers ( Vo), premaxillaries, maxiUary, 

 and palatiTie (PI) bones. 



The lower jaw is composed of two rami, united in the middle 

 hne in front by a symphysis, each half bearing teeth (IM). The 

 lower jaw articulates with the skull at its posterior end. 



The ribs, of which there are eighteen, rarely nineteen, pairs, 

 form a kind of box in which are lodged some of the organs of 

 the body, which they protect, especially the respiratory organs 

 and heart. Each rib articulates with two vertebrae. The end of 

 the rib nearest the vertebrae has two heads — one the capitulum, 

 the other the tuberculum. The front ribs are flattest, and as 

 they pass back they become more and more arched. A rib 

 consists of two portions — the true bony rib, which unites with 

 the vertebrae, and a cartilaginous portion, the costal cartilage, 

 which unites the rib with the sternum or breast-bone. The first 

 eight pairs of ribs unite with the sternum separately by their 

 costal cartilages. The other ten pairs have their costal cartilages 

 united, and meet all together with the "breast-bone.'' The 

 former are the true ribs, the latter the false ribs. The breast- 

 bone or sternum, with which the ribs unite, is a narrow keel- 

 shaped bone, partly composed of cartilage. 



The anterior arch and limb are closely united by a distinct 

 articulation forming a ball-and-socket joint. Nevertheless the 

 fore-limb of the horse is not able to completely rotate, as is the 

 case with the human arm. The anterior or pectoral arch is 



