LIGAMENTS OF THE VERTEBRAL COLUMN. 253 
It is not necessary to suppose that the synovial membrane has disappeared from these 
articular cartilages as the result of friction, because, notwithstanding constant friction, 
such parts as the interior of capsular ligaments or the semilunar cartilages of the knee- 
joint have not been denuded of their synovial covering. 
MORPHOLOGY OF LIGAMENTS. 
From what has been said in connection with the development of joints, it will be evident 
that ligaments are essentially products derived from the cellular articular disc. 
Nevertheless, in relation to the fully-formed joint, many structures are described as ligaments, 
which do not take origin in the manner just indicated. Some of these ligamentous structures 
remain fairly distinct from the capsular ligaments with which they are immediately associated ; 
others become thoroughly incorporated with the capsular ligaments and cannot be separated 
therefrom, while yet others may be found situated within the capsule of a joint, and thus play 
the part of interarticular ligaments. 
Instances of each of these forms of adventitious ligaments may be readily given. For 
example, we may instance the expansion of the tendon of the semimembranosus muscle to the 
posterior ligament of the knee-joint, and the offshoots from the tendon of the tibialis posticus 
muscle to the plantar aspects of various tarsal bones, as illustrations of structures which play 
an important part as ligaments, but are not indelibly incorporated with the joint capsule. 
Of structures which have become indelibly incorporated with the primitive capsule, we may 
instance the broad tendinous expansions of the quadriceps extensor muscle around the knee-joint. 
The internal lateral ligament of the same joint is regarded as a detached portion of the 
tendon belonging to that part of the adductor magnus muscle which takes origin from the 
ischium, while the external lateral ligament of the knee is considered by some to be the primi- 
tive femoral origin of the peroneus longus muscle. Another illustration of the same condition 
is found in the coraco-humeral ligament, which is regarded by some as representing a detached 
portion of the pectoralis minor muscle. 
Two illustrations may be given of structures playing the part of ligaments within the 
capsule of a joint, although in the first instance they are not developed as ligaments. It is 
questionable if the ligamentum teres of the hip-joint is an interarticular ligament in the true 
sense of the term; it has been regarded as the isolated and displaced tendon of the ambiens muscle 
found in birds. In the shoulder-joint, many observers look upon the superior gleno-humeral 
ligament as representative of the hgamentum teres. 
Such structures as the stylohyoid ligament and the internal lateral ligament of the temporo- 
mandibular joint, although described as ligaments, are in reality skeletal parts which have not 
attained their complete ossific development. 
Again, certain portions of the deep or muscular fascia of the body which become specialised 
into restraining and supporting bands (e.g. the ilio-tibial band of the fascia lata ; the stylo-mandi- 
bular ligament; the anterior and posterior annular ligaments of the wrist-joint ; the anterior, 
inner, and outer annular ligaments of the ankle - joint), although called ligaments, have no 
direct developmental association with articular ligaments. 
4 Lastly, the ligament of Poupart and the ligament of Gimbernat, being special developments 
in connection with an expanded tendon or aponeurosis, are still further removed from associa- 
tion with an articulation. 
All vertebree, with the exception of those which deviate from the common 
vertebral type, present two sets of articulations whose various parts are arranged 
upon a uniform pattern. Thus every pair of typical vertebra presents an articula- 
tion between the centra, termed intercentral, and a pair of articulations between 
the neural arches, called interneural. With the latter there are associated various 
important accessory ligaments which bind together laminz, spinous processes, and 
transverse processes. 
Intercentral Articulations.——These are amphiarthrodial joints. Singly, they 
present only a slight degree of mobility, but when this amount of movement is 
added to that of the whole series, the range of movement of the spine becomes 
considerable. The articular surfaces are the flattened surfaces of adjacent vertebral 
bodies. They are bound together by the following structures :— 
Intervertebral Discs (fibro-cartilagines intervertebrales, Fig. 198).—EKach disc 
accommodates itself to the space it occupies between the two vertebral bodies, to 
both of which it is firmly adherent. The discs, from different parts of the spinal 
column, vary in vertical thickness, being thinnest from the third to the seventh dorsal 
vertebra, and thickest in the lumbar region. In the cervical and lumbar regions 
each disc is thicker in front than behind, thereby assisting in the production of the 
. 
. 
LIGAMENTS OF THE VERTEBRAL COLUMN AND SKULL. 
4 
