TEE VMSTEBRAL COLUMN. 



29 



Direction of the vertebral column. — The spine does not extend in a 

 straight line from the head to the posterior extremity of the body. If it 

 is followed from the caudal termination, which is free and looks downwards 

 to the anterior extremity, it will be seen that it rises upwards and forwards' 

 forming a convex inflexion corresponding to the roof of the pelvis. In 

 the lumbar and the posterior half of the dorsal region it is nearly horizontal 

 and rectilinear ; from thence it descends to the cervical region, when it 

 again rises and forms two curves, the one posterior, bending upwards, the 

 other anterior, turned down. This disposition of the cervical spine gives 

 it the shape of a console. 



Mobility of the vertebral column. — In the cervical region, the almost total 

 absence of spinous processes, the great development of the articular 

 processes, and the very short curve described by the surfaces of contact 

 of the vertebral bodies, allows the spine very extensive and very diverse 

 movements. In the dorsal region, however, these movements are very 

 limited, the spinous processes and the costal arches preventing the play 

 of the vertebras on each other. In the lumbar region, the spine can be 

 flexed or extended more than in the dorsal ; but its lateral movements are 

 quite as restricted, owing to the presence of the transverse processes and 

 the reciprocal joining or dovetailing of the articular processes. Lateral 

 motion is even rendered impossible in the posterior half of this region, 

 from the manner in which the transverse processes are adapted to each other. 

 It may be remarked, however, that this disposition singularly favours the 

 integral transmission of the propulsive efforts thrown upon the trunk by 

 the posterior extremities. 



The sacral vertebrre, having to afford the ossa innominata a solid fixed 

 point, could not preserve their independence and mobility, and are conse- 

 quently consolidated into a single piece which fulfils all its requirements 

 in this respect. In the coccyx the rachidean stalk again recovers its 

 mobility, and to a degree more marked than elsewhere ; the coccygeal bones, 

 articulated with each other by means of convex surfaces, and deprived of 

 long processes at their extremities, are placed in the best possible conditions 

 for variety and extent of movement. 



DIFFEKENTIAL CHAEACTEBS IN THE VERTEBRAL COLUMN OF OTHER THAN 

 SOLIPED ANIMALS. 



The Number of Pieces composing the Spine slightly varies in the Domesticated 

 Animals, as will be seen in the following Table. 



A. Vertebrae op the Ox, Sheep, and Goat.— 1. Cervical Vertebra. — The cervical 

 vertebra of the Ox differ from those of solipeds by their shortness and the greater deve- 

 lopment of their insertion eminences. In the Sheep and Goat they are relatively longer, 

 than in the Ox. The transverse processes of the atlas are less inclined than in the Horse, 



