JOINTS AND LIGAMENTS. 39 



passage of tendons ; and interosseous ligaments bind bones closely 

 together. Besides these, there are suspensory and check ligaments, which, 

 as far as we are at present concerned, are respectively represented by 

 the structures, bearing these names, which are found in the legs, below 

 the knees and hocks. 



The ligaments to which I have referred are, like tendons, composed of 

 white fibrous tissue (a variety of connective tissue, p. 30), which is 

 hard, strong, and inelastic. Yelloiv ligaments are, without going into 

 minute differences, to be distinguished by the fact of their yellow colour, 

 and by the possession of considerable elasticity, which enables them 

 to passively bear weights which would otherwise fall on the muscles. 

 A famihar instance of the manner in which elastic ligaments mechanically 

 save the expenditure of muscular force, is afforded by the arrangement 

 which keeps the claws of a cat retracted without entailing exertion on 

 the animal ; each claw being kept back by a small elastic ligament, 

 which becomes stretched when the digits of the paw are extended by 

 their muscles. As soon as these muscles cease to act, the ligaments, 

 by their power of contraction, regain their natural length and draw in 

 the claws. An enormously powerful elastic ligament is attached to the 

 withers, and goes straight from them, in the form of a cord, to the top 

 of the head (the bony prominence between the ears), to which it is in- 

 serted. At about a third of. the distance from the head to the withers, 

 a broad sheet of elastic tissue is given off from the corded portion, and 

 is united to all the spines of the neck vertebrae, 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 called the ligamentum nuchcB, or suspensory 

 ligament of the head and neck. It is continuous with the strong, 

 white fibrous ligament which commences on the spines of the sacrum 

 and runs along the top of the spines of the vertebrae 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 its top there is a layer of fat, which in entires (especially 

 if they are coarsely bred) often increases to a great size, and 



