24 



OSTEOLOGY 



A trochlea is a pulley-like articular mass. 



A glenoid cavity (Cavitas glenoidalis) is a shallow articular depression, and a 

 cotyloid cavity or acetabulum is a deeper one. 



The term facet is commonly applied to articular surfaces of small extent, 

 especially when they are not strongly concave or convex. 



The terms fossa, fovea, groove or sulcus, and impression are applied to various 

 forms of depressions. 



A foramen is a perforation for the transmission of vessels, nerves, etc. 



A sinus or antrum is an air-cavity. 



Other terms, such as canal, fissure, notch, etc., recjuire no explanation.^ 



VERTEBRAL COLUMN 



The vertebral column (Columna vertebralis) is the fundamental part of the 

 skeleton. It consists of a chain of median, unpaired, irregular bones which 

 extends from the skull to the end of the tail. In the adult certain vertebrae have 



become fused to form a single bony mass 

 with which the pelvic girdle articulates. 

 Vertebrae so fused are termed fixed or 

 "false" vertebrae (Vertebra? immobiles), as 

 distinguished from the movable or "true" 

 vertebrae (Vertebrae mobiles). 



The column is subdivided for descrip- 

 tion into five regions, which are named ac- 

 cording to the part of the body in which 

 they are placed. Thus the vertebrae are 

 designated as cervical, thoracic (or dorsal), 

 lumbar, sacral, and coccygeal or caudal 

 (Vertebrae cervicales, thoracales, lumbales, 

 sacrales, coccygeae). The number of verte- 

 brae in a given species is fairly constant in 

 each region except the last, so that the ver- 

 tebral formula may be expressed (for the 

 horse, for example) as follows: 

 CyTigLgSjCyjj.^j. 

 The vertebrae in a given region have 

 special characters by which they may be 

 distinguished from those of other regions, and individual vertebrae have characters 

 which are more or less clearly recognizable. All typical vertebrae have a common 

 plan of structure, which must first be understood. The parts of which a vertebra 

 consists are the body or centrum, the arch, and the processes. 



The body (Corpus vertebrae) is the more or less cylindrical mass on which the 

 other parts are constructed. The anterior and posterior extremities of the body 

 are attached to the adjacent vertebrae by intervertebral fibro-cartilages, and are 

 usually convex and concave respectively. The dorsal surface is flattened and enters 

 into the formation of the vertebral canal, while the ventral aspect is rounded 

 laterally, and is in relation to various muscles and viscera. In the thoracic region 

 the body presents two pairs of demifacets (Foveae costales) at the extremities for 

 articulation with the heads of two pairs of ribs. 



The arch (Arcus vertel^rae) is constructed on the dorsal aspect of the body. 

 It consists originally of two lateral halves, each of which is considered to consist 

 of a pedicle and a lamina. The pedicles form the lateral parts of the arch, and are 



'As might be expected from the history of anatomy, a good many of tliese terms are more or 

 less interchangeable; furthermore, a given skeletal feature may differ greatly in various species. 



Trojisv. 



fiuief 



Fig. 4. — First Thoracic Vertebr.e of Horse 

 To illustrate plan of structure of vertebrje. 



