ANATOMY. 19 



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

 irregularly shaped flat bones, the most important of which is the 

 cranium, or brainpan, occupied by the brain and communicating 

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

 through the center of the cervical, dorsal, lumbar, sacral, and some- 

 times the first two or three coccygeal vertebrae. The orbital cavities 

 (containing the eyes) communicate with the brain by narrow pas- 

 sages, through one of wliich 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, arid separated 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) boundary 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 

 spa^e. 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 segments 

 firmly united in front and spreading backward somewhat in the form 

 of a letter V. 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 corre- 

 spond 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; humerus, 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, cannon bone ; two small metacarpals, 

 splint bones (the three metacarpal bones are joined together, forming 

 the metacarpus); two sesamoids, pulley bones; os suffraginis, upper 

 pastern bone; os corona, lower pastern bone; os pedis, coffin bone, 

 and OS navicularis, shuttle bone. The scapula is extended by means 

 of a thin plate of gristle, called the " caHilage of prolongation," which 

 offers additional attachment for the muscles of the body. 



