54 THE HEAD. 



the neck, fvdthout touching it, and then, attaching itself strongly 

 to the second bone, principally supports the head by its union 

 with this bone. The mechanical disadvantage is increased ; but 

 the head is turned more freely on the first and second bones 

 The principal stress is on the dentata or second bone, so much 

 80, that in poll-evil, this ligament may be divided vidthout sori- 

 ous inconvenience to the horse. It then suddenly sinks deeper, 

 and communicates with all the other vertebrae. Each of these 

 communications becomes a separate point of support, and as they 

 approach nearer to the base, the mechanical disadvantage, or 

 the force with which the weight of the head and neck presses 

 and acts, is materially lessened. 



The head, then, while the animal is in a state of rest, is sup- 

 ported by this hgament, without any aid from muscular energy. 

 It differs from the other ligaments of the body, in the fact 

 that it is elastic. It stretches full two inches longer when the 

 horse is browsing, and resumes its natural dimensions when the 

 head is held erect. 



The ligament of the neck is inserted into the centre of the 

 back part of the oocipita,! bone, and immediately below the 

 vertex or crest of that bone ; and therefore the bone is so thick 

 at this part (see fig. e, Fig 3). 



Many large and powerful muscles are necessary to turn the 

 head in various directions, as well as to assist in raising it when 

 depressed. The occipital bone, as will be seen in the cut, pre- 

 sents a spine running down the centre, B, and a large roughened 

 surface for the attachment of these muscles, C C. 



Lower dovm, and still at the 

 back of the occipital bone, are 

 two rounded protuberances D D, 

 by which the head is coimected 

 with the atlas, or upper or first 

 vertebra, or bone of the neck ; 

 and these are called the condy- 

 loid, cup-shaped, processes of the 

 occipital bone. AU the motions 

 of the head are partly, and many 

 of them wholly, performed ' by 

 this joint. 



Between them is a large hole, 

 the foramen magmrni, or great 

 aperture, E, through which the continuation of the brain, termed 

 the spinal cord or marrow, passes out of the skull. 



As an additional contrivance to support the enormous weight 

 of the head, are two other projections of the occipital bone, pe- 

 culiar to aniinals whose heads are set on in a slantin? direction. 



