350 THE ANATOMY OF THE HORSE 



which all the other parts are framed. At its first appearance it is a 

 cartilaginous cylinder, surrounding and protecting the primitive trace of the 

 nervous system ; but as the embryo increases in growth, points of ossification 

 are developed corresponding to each vertebra, the whole tube being finally 

 divided into distinct pieces called vertebrce, to which the bones of the head 

 are a prolongation, corresponding in their nature, though difiering out- 

 wardly in form. 



The vertebrce are divisible into true and false, the former reaching from 

 the head to the pelvis, and the latter extending thence backward, being 

 respectively called the sacram and coccyx. 



The true vertebrce comprise the 7 cervical, 18 dorsal, and 6 lumbar 

 vertebi'se. Each consists of a body, from which two laminpe or plates project 

 upwards, terminating in a spinous process. In addition to these are two 

 lateral projections (transverse processes), which serve the purpose of firmly 

 connecting the vei'tebrre together by means of the muscles attached to 

 them, and. also to the ribs and extremities below. Lastly, each vertebra 

 has two small surfaces before . and the same number behind (articular 

 surfaces), which form distinct joints between them. The details of these 

 parts, and the peculiarities met with in each set, will be described in the 

 next chapter. 



Between the body, the laminae, and the spinous process is an opening 

 more or less triangular in shape, in which lie the spinal cord and its 

 investments. The edges of this opening are attached to those before and 

 behind by ligamentous tissues {ligamenta siibjlavct), which, opposite each 

 intervertebral space, are pierced by openings on each side to give exit to the 

 vertebral nerves passing out to the exterior of the body and to the ex- 

 tremities. Opposite to these openings the bone is notched above and below, 

 and these hitervertebral notches complete the parts common to the whole 

 series. Thus the vertebral or spinal column serves as a firmly secured 

 but flexible tube for the lodgment of the spinal cord, while at the same 

 time it gives passage to its nerves. By this formation it is far less liable 

 to injur}'^, and also more useful as an aid to locomotion, than if it were made 

 of one solid piece of bone, which, from its length, would be readily broken. 



OF THE HEAD AND FACE, AND OF THE HYOID 

 ARCH 



Modern anatomists, following out the idea first suggested by Maclise 

 and Owen, consider the head as made up of six vertebrae ; the posterior one, 

 or that nearest to the neck, being the occipital bone, the next two being 

 made up of the temporal bone, and the ultimate vertebrae consisting of the 

 sphenoid and aethmoid bones. This is a somewhat fanciful hypothesis, when 

 worked out in detail ; but it is obvious that the several bones of the skull 

 subserve the same purposes as the vertebrae, and resemble those parts of the 

 skeleton in forming a series of irregular arches to protect the brain, the 

 division into separate pieces being far more secure than if the whole were 

 in one. 



The boxes of the face, including the lower jaw and os hyoides, depend 

 from the neural arch or brain-case much in the same way as the ribs and 



