588 A MANUAL OK VETERINARY PHYSIOLOGY 



the animal to sleep in the standing position while the muscles 

 rest. They are known as check ligaments. Another kind of 

 ligament peculiar to quadrupeds is a tendo-ligament — i.e., a 

 muscle with a tendon running completely through its substance 

 from origin to insertion, which, when the muscle is not actively 

 contracting, acts as a ligament, and when it is contracting 

 plays its normal part of tendon. We shall see that this mechanism 

 is employed both in the fore and hind legs for the purpose of 

 maintaining a standing attitude with as little muscular strain as 

 possible. A muscle may furnish a ligament to another muscle 

 in order to afford it support. This is shown in the ligament 

 detached by the biceps brachii (flexor brachii) to the extensor carpi 

 radialis (extensor metacarpi magnus). A variation of this is a 

 muscle detaching a ligament to a bone which is considerably out 

 of its path — for instance, the ligament detached by the large 

 biceps femoris (triceps abductor femoris) to the calcis.* 



The elasticity of tendons and ligaments is considered later 

 (p. 607). This feature has proved a fruitful source of difference 

 of opinion, and the matter is by no means agreed upon. 



The elasticity of muscle has been dealt with at p. 401, and to 

 form a conception of what occurs to tendons under the influence 

 of strain, the elastic property of muscle must not be lost sight 

 of. Nothing could well be more unlike in appearance, texture, 

 and general physical characters, than muscle and tendon. Yet 

 the soft, pulpy, friable material does not tear in the living 

 animal, while the tendon attached to it may be torn apart. 

 The only locomotor muscle in the horse's body which shows a 

 disposition to rupture is the flexor metatarsi, and such a lesion is 

 so rare that many have never seen it. 



Colin tested the breaking-strain of muscles removed from a horse 

 which had just been destroyed. The great extensor of the meta- 

 carpus broke at a tension of 988 kilogrammes (2,173 pounds) ; the 

 flexor perforans of the fore-limb at 685 kilogrammes (1,507 pounds) ; 

 and the flexor of the arm at 973 kilogrammes (2,140 pounds). In 

 the hind limb the extensor pedis muscle broke at 415 kilogrammes 

 (913 pounds), the flexor of the metatarsus at 924 kilogrammes 

 (2,032 pounds), and the flexor perforans at 510 kilogrammes (1,122 

 pounds). The extensors of the metatarsus ruptured at 616 kilo- 

 grammes (1,355 pounds), 687 kilogrammes (1,511 pounds), and 

 983 kilogrammes (2,162 pounds) respectively, but the muscles are 

 not mentioned by name. It will be observed that the breaking- 

 strain of the extensors is much higher than that of the flexors, that 

 of the extensor of the metacarpus being nearly one ton. In the 

 hind-limb there is a marked difference between the breaking-strain 



* Anatomists are responsible for the confusion existing in muscle 

 nomenclature. Where possible, the writer has followed Sisson in modern 

 terminology, inserting the known equivalent in brackets. There are six 

 names for the biceps femoris muscle ! 



