250 COMPARATIVE ARTHROLOGY 
ment of ligaments which connect the small digits with each other and with the 
chief digits (Fig. 258). 
This apparatus is somewhat complex, but its chief features are as follows: A proximal inter-~ 
digital ligament is attached on either side to the third phalanges of the small digits, while centrally 
it blends with the annular ligaments of the flexor tendons behind the metacarpo-phalangeal 
joints of the chief digits. Two bands (central longitudinal interdigital ligaments) arise on the 
bases of the small digits, cross the flexor tendons obliquely downward and centrally, pass through 
the proximal interdigital ligament, and blend below with the distal interdigital ligament. Two 
collateral bands (collateral longitudinal interdigital ligaments) are attached in common with the 
proximal interdigital ligaments to the third phalanges of the small digits, and blend below with 
the outer part of the distal interdigital ligament. 
Dog.—Each joint has a capsule and two collateral ligaments. The distal 
joints have also two elastic dorsal ligaments (Ligg. dorsalia), which extend from 
the proximal end of the second phalanx to the ridge at the base of the third 
phalanx. They produce dorsal flexion of the joint, and thus raise or retract the 
claws when the flexor muscles relax. The distal sesamoids are represented by 
compiementary cartilages attached to the volar margins of the articular surfaces 
of the third phalanges. 
Three interdigital ligaments restrict the spreading apart of the digits (Fig. 259). 
Two of these cross the volar surface of the proximal parts of the chief digits, 7. e., 
one for the second and third, the other for the fourth and fifth; they blend with the- 
annular ligaments on either side. The third ligament is attached on either side to 
the foregoing ligaments and the annular ligaments of the third and fourth digits, 
and curves downward centrally, ending in the large pad on the paw. 
ARTICULATIONS OF THE PELVIC LIMB 
SACRO-ILIAC JOINT 
This joint and the pelvie ligaments present no very striking differences in the 
other animals except that the sacro-sciatic ligament in the dog is a narrow but 
strong band which extends from the posterior part of the lateral margin of the 
sacrum to the tuber ischii; it is the homologue of the ligamentum sacro-tuberosum 
of man. 
HIP JOINT 
Ox.—The shallowness of the acetabulum is compensated by the greater size 
of the marginal cartilage, which is specially large laterally. The head of the femur 
has a smaller radius of curvature than that of the horse, and the articular surface 
extends a considerable distance outward on the upper surface of the neck. The 
round ligament is entirely intra-articular; it is small, and sometimes absent. The 
accessory ligament is absent. 
There are no important differences in the other animals. 
STIFLE JOINT 
Ox.—There is a considerable communication between the femoro-patellar 
and medial femoro-tibial joint cavities; this is situated as in the horse, but-is wider. 
A small communication with the lateral femoro-tibial capsule sometimes occurs. 
The two femoro-tibial capsules usually communicate. The middle patellar liga- 
ment is not sunken, as there is no groove on the tuberosity of the tibia where it is 
attached. The lateral patellar ligament fuses completely with the tendon of in- 
sertion of the biceps femoris, and a large synovial bursa is interposed between them 
and the lateral condyle of the femur. - i 
Pig.—The femoro-patellar capsule is strongly reinforced on both sides by bands . 
