MORPHOLOGY OF LIGAMENTS 281 



At the interphalangeal joint of the great toe there is very frequently a small 

 sesamoid bone whicli plays on the plantar surface of the first i)halanx, in the same 

 way as the sesamoid l)ones of the metatarso-plialangeal joint play upon the plantar 

 surface of the head of the metatarsal bone. 



Morphology of lAgaments 



The various ligaments of the human body have, in very many instances, been evolved as the 

 result of secondary changes in muscles adjacent to joints. In a few instances, ligaments repre- 

 sent the degenerate remnants of cartilaginous and bony elements. 0a])sular ligaments are in most 

 joints derived from the periosteum, but they may be strengthened by the incorporation of tendons 

 detached from adjacent muscles. 



Muscles arising from, or inserted into bones in tlie immediate vicinity of a joint tend to 

 become metamorphosed into tendon near their attachments, and a comprehensive study of 

 myology in low vertebrate forms indicates that thei'e is associated with this tissue-change a 

 tendency for the muscle to alter its point of attachment ; hence a muscle originally inserted below 

 a joint may eventually come to have its insertion above the joint. In the same way, a muscle 

 arising above a joint may, as a result of altered environment, sbitt its origin to some point below 

 the joint. To this change of position the term migration of muscles has been applied. In many 

 instances a portion of the muscle equivalent to the distance between the original and the acquired 

 attachment ])ersists as a fibrous band and fulfils the function of a ligament. This is well seen in 

 the knee-joint, where the internal lateral ligament is derived from the adductor magnus, this 

 muscle having shifted its insertion from the tibia to the femur. In the same waj* the external 

 lateral ligament represents the tendon of the peroneus longus, which has migrated from the 

 femur to the head of the fibula. 



One of the most remarkable examples of a tendon divorced in this way is the ligamentum 

 teres in the hip-joint. This curious structure was in all probability the tendon of the pectineus, 

 which has been detached from the muscle in consequence of the profound alterations which have 

 taken place in the limb during its evolution. 



Among other ligaments derived in a similar way from muscles may be mentioned the greater 

 sacro-sciatic ligament. This was originally the tendon of origin of the biceps femoris. (H. 

 Morris, "A Note on Three Points in Anatomy," Med. Times and Gazette, April 7, 1S77, p. 361.) 

 The lesser sacro-sciatic is derived from the fibrous retrogression of portions of the coccygeus. The 

 sacro-coccygeal ligaments represent the muscles which lift, depress, and wag the tail in those 

 mammals furnished with such an appendage ; indeed, these ligaments are occasionally replaced 

 by muscle-tissue. 



The coraco-humeral ligament is derived from the original tendon of insertion of the pectoralis 

 minor, and not unfrequentl.y the muscle is inserted into the lesser tuberosity of the humerus, the 

 ligament being then replaced by the tendon of the muscle. The coraco-clavicular, rhomboid, and 

 gleno-humeral ligaments are probably derived from modifications of the subclavius mu.scle. 



The vertebral column contains several ligamentous structures of great morphological interest. 

 The pulpy substance in the centre of each intervertebral disc is derived from the notochord ; the 

 suspensory ligament passing from the tip of the odontoid process to the anterior margin of the 

 foramen magnum is a remnant of the sheath of the notochord, and indicates its position as it 

 passed from the vertebral column into the base of the cranium. The transverse ligament of the 

 atlas (as pointed out by Professor Cleland in 1859 and 1861), is a persistent and functional form 

 of the posterior conjugal ligament uniting the rib-heads in seals and many other mammals, whilst 

 the interosseous ligament of the head of a rib in man is the feeble representative of this structure 

 in the thoracic region of the spine. The ligamentum conjugale costarum was described by Mayer 

 in 1834 (Archives d' Anatomic de Muller). According to Luschka's account of this ligament it 

 would seem as though the po.sterior .superior fibres of the capsule of the costo-central joint repre- 

 sented it in man, rather than the interos.seous ligament. 



Many of the subcutaneous tracts of fascia and many aponeuroses in the human body are 

 derived from the metamorphosis and retrogression of muscle-tissue. 



