20 THE ARMY HORSE. 



The skull, containing cavities (or chambers), is composed of 

 irregularly shaped flat bones, the most important of Avhich is 

 the cranium, or brainpan, occupied by the brain and communi- 

 cating with the bony canal (containing the spinal cord), which 

 passes through the center of the cervical, dorsal, lumbar, sacral, 

 and sometimes the first two or three coccygeal vertebrae. The 

 orbital cavities (containing the eyes) communicate with the 

 brain by narrow passages, through one of which the optic 

 nerve passes. 



On each side, below the eye, are two closed cavities known as 

 the superior (upper) and inferior (lower) maxillary sinuses,' 

 in the lower third of the skull are found the nasal chambers 

 extending from the nostrils backward to the pharynx, and sep- 

 arated by a thin partition of bone and cartilage, called the 

 septum nasi; the floor of these chambers forms the roof of the 

 mouth. From the orbital cavities the skull gradually becomes 

 narrower and terminates a short distance below the nostrils in 

 the premaxilla, which contains the six upper incisor teeth; 

 these six, with the corresponding teeth in the lower jaw, form 

 the anterior (front) boundarv of the mouth, which extends 

 back to the pharynx. On the upper portion of the back of the 

 mouth cavity are found six molar or grinder teeth on each side ; 

 that portion of the jaw between them and the incisors is called 

 the interdental space. Situated on each side near the incisor 

 teeth in this space are found, in the male, and rarely in the 

 female, the tushes or canine teeth. 



The inferior maxilla or lower jaw is composed of two seg- 

 ments firmly united in front and spreading backward some- 

 what in the form of a letter Y. Each branch, at the end, 

 turns upward and is united to the skull proper in a movable 

 joint. The branches of the jaw include a space appropriately 

 called the maxillary space. Located in the united or front part 

 of this bone are the inferior incisors and canine teeth, and, in 

 the branches, the inferior molars, which correspond to those of 

 the upper jaw. The space between the molars and incisors is 

 the same as that in the upper jaw. 



The front leg is composed of the following bones, named in 

 order from above downward: Scapula, shoulder blade; hu- 

 merus^ bone of the arm ; radius, bone of the forearm, and ulna, 

 bone of the elbow (radius and ulna are united in one bone) ; 

 carpus, knee bones (seven small bones) ; large metacarpal, can- 

 non bone; two small metacarpals, splint bones (the three nieta- 



