42 OUTLINES OF EQUiyE ANATOMY. 



fangs of tlie molars as far as the anterior maxillary fora- 

 men, where each sends a branch outwards, while the main 

 portion continues on in the bone to supply the incisors 

 and tush. The upper edge of the internal surface up 

 against the molar teeth is termed the alveolar ridge, and 

 affords attachment to mylo-hyoideus, the external surface 

 of which muscle lies in contact with the bone as far down 

 as the inferior margin, where the submental branch of the 

 submaxillary artery passes forwards, just abovethe attach- 

 ment of digastricus. Below this the inferior margin of the 

 bone is rounded and covered with panniculus ; at the com- 

 mencement of the ramus it presents one or more promi- 

 nences, which serve to mark where the submaxillary vessels 

 and the parotid duct wind round the jaw. 



THE VERTEBRA. 



The distinctive characteristic of vertebrata is the pos- 

 session of a central chain of bones forming a spinal column. 

 The chain is composed of vertebrae, and to the vertebrae 

 all the other bones of the body are appended, so that each 

 vertebra with its bony appendages constitutes a vertebral 

 segment of the body. These vertebral segments differ in 

 number in different animals, and frequently vary in animals 

 of the same species. They are between fifty and sixty in 

 number in the horse. A complete or typical vertebral 

 segment consists of two similar arches united in forming 

 a rounded body or centrum. One is placed superiorly to 

 the centrum, and as it encloses the nerve-centres of animal 

 life is termed the neural arch; the other is inferiorly 

 placed, and is termed the hcemal arch, — it encloses the 

 organs of vegetative life, including circulation, respiration, 

 digestion, and involuntary motion. Each arch may be 

 divided into five parts ; those of the neural arch are : 

 pedicles, running upwards from the supero-lateral parts 

 of the body ; lamince, running from the upper extremities 

 of the pedicles to meet in the central line, and from the 

 point of junction the neural or superior spinous process runs 

 upwards. These parts may be found in almost all the 

 vertebral segments, though only in a rudimentary con- 

 dition in the coccygeal region. The haemal arch can be 

 recognised only in the dorsal, though found under ex- 

 treme modification in most of the other regions. Here 



