28 SKETCH OF THE ANATOMY OF THE HORSE. 



and is united to all the spines of the neck vertebrre, except the first. This 

 sheet accordingly acts as a partition between the muscles on the respective 

 sides of the upper part of the neck. The entire ligament, therefore, by its 

 strength and elasticity greatly aids the muscles in supporting the weight of 

 the head and neck. The amount of stretching which it can undergo in 

 ordinary circumstances may be approximately estimated by comparing the 

 length of the neck, when the head is held up in its usual position, to that 

 when it is lowered to allow the animal to feed off the ground. In the first 

 case, with a horse 15.3 high, it will probably not exceed 28 inches in 

 length; but in the latter it must be over a yard long, supposing that the 

 animal does not unduly bend his knees. Any depression or elevation 

 beyond the position occupied by the head when the horse is asleep standing, 

 has to be obtained by muscular force. This ligament is popularly called the 

 J}ackwax. Without being pedantic, we might, I think, more appropriately 

 term it the suspensory ligament of the head and neck I may add that it is 

 continuous with the strong, white fibrous ligament which commences on the 

 spine of the sacrum and runs along the top of the spines of the vertebrse of 

 the loins and back, binding them together, until it nearly reaches the summit 

 of the withers, where its fibres assume the character of yellow elastic tissue. 

 On the top of this large ligament there is a layer of fat, which in entires 

 (especially if they be coarsely bred) often increases to a great size, and 

 consequently gives them a high and thick crest (Fig. 263). The intestines of 

 the horse are supported by the abdommal tunic^ which covers the muscles 

 of the lower part of the belly, and consists of a broad, strong sheet of 

 yellow elastic tissue. It acts like an elastic abdominal belt. 



There is considerable power of movement between the head and the first 

 vertebra of the neck (the atlas), and between the diiferent neck vertehrce 

 themselves; but hardly any between the dorsal vert:brce. The loin vertebrm 

 can be flexed and extended to a slight degree on each other; but are 

 capable of only very little motion from side to side. The sacrum, as before 

 mentioned, forms in the adult horse a single bone, on which the pelvis rests, 

 and with which it is connected by powerful ligaments that greatly restrict its 

 movements on the spine. We have also seen that the thigh bones articulate 

 with the pelvis. The bones of the tail possess considerable mobility. The 

 solid connection thus afforded to the hind limbs, with the trunk, enables the 

 former to transmit to the latter the forward impetus given during progression 

 with the least possible loss of power. The capability of the loins to be flexed 

 and extended is necessary in order to facilitate the action of the loin muscles, 

 which are important agents in locomotion (p. 52). The mobility of the 

 head, neck, and, to a much lesser degree, of the tail, acting as they do 

 as balancing poles, is extremely useful in enabling the animal to perform with 

 ease and precision many of the varied and difficult movements demanded of 

 him. We may see that any power of lateral motion which the trunk (not 

 counting the head, neck and tail) may possess, however much it may make 

 the horse quick and " handy " at turnnig, will militate against his speed in a 

 forward direction. 



