212 TEE ARTICULATIONS. 



pulleys by which the two phalanges correspond : an arrangement that permits the claw to be 

 lodo'ed between two digits wlien they are raised, and tlius favour its retraction. 



Tlie second iuteiphalangeal articulation of the Dog and Cat is also distinguished by another 

 essential arrangement. The articular surface of the third phalanx is completed by a glenoid 

 fibrocartiiage analogous to that of the first articulation, but much thicker. This fibro-cartilage 

 (see Muscles of the Hand) is fixed into the posterior projection of the third phalanx, and 

 serves, by its inferior face, as a pulley for the perforaus tendon and, with the projection just 

 named, plays the part of the navicular bone in other animals. 



The interphalangeal articulations of Man are formed on the same plan as the metacarpo- 

 phalangeal articulations They are consolidated by a glenoid and lateral ligaments, and 

 possess only the two movements oi flexion and extension. 



Article V. — Articulations of the Posterior Limbs. 

 1. Articulations of the Pelvis. 



{Preparation.— These ligaments are all exposed to view by carefully removing the soft parts 

 connected with the sacrum and coxae.) 



A. Sacro-iliac Articulation (Figs. 139, 140).— This is a pair articulation 

 which establishes the union of the posterior limb with the spine, and is formed 

 by the sacrum and coxa. It belongs to the arthi'odial class. 



Articular surfaces. — On the sacrum, the irregular diarthrodial facet named 

 the " auricular," cut on the sides and near the base of the bone. For the coxa, 

 the analogous facet on the internal face of the ilium. 



3fode of union. — By four ligaments, which, after the example of Rigot, we 

 will name sacro-iliac, superior ilio-sacral, inferior ilio-sacral, and the sacro-sciatic. 

 The first is situated immediately around the articular surfaces, and the others are 

 only in mediate relations with them. 



a. Sacro-iliac ligament (Fig. 140, 1). — This is composed of thick fibrous 

 fasciculi, which envelop the whole articulation in being firmly attached by their 

 extremities, to the imprints around the diarthrodial facets. The inferior moiety 

 of this ligament is covered by the iliacus muscle. Its posterior half ^ is much 

 stronger, is hidden by the ilium, and gives attachment to the longissimus dorsi 

 muscle. 



h. Superior ilio-sacral ligament (Fig. 139, 13). — A thick and short funicle, 

 which, rising from the internal angle of the ilium, is carried backwards to be 

 fixed to the sacral spine, where its fibres are confounded with those of the super- 

 spinous dorso-lumbar ligament. 



c. Inferior ilio-sacral ligament (139, 14).— This is very resisting, triangular, 

 membranous band, formed of parallel fibres passing obliquely downwards and 

 backwards. It is attached, by its anterior margin, to the upper half of the 

 sciatic border and the internal angle of the ilium, in becoming confounded with 

 the preceding ligament. Its inferior margin is inserted into the rugged lip which 

 borders the sacrum laterally. Its posterior border is united to the aponeurosis 

 covering the coccygeal muscles, and its external face is in contact with the 

 principal gluteal and the long vastus muscles ; while the internal lies against the 

 lateral sacro-coccygeal muscle. 



d. Sacro-sciatic or ischiatic ligament (Fig. 140, 2).— This is a vast membranous 

 expansion situated on the side of the pelvis, between the sacrum and the coxa. 

 It serves more as a means for enclosing this portion of the pelvic cavity, than to 

 assure the solidity of the sacro-iliac articulation. Its form is irregularly quadri- 



' It represents the interosseous sacro-iliac ligament of Man. The inferior half corresponds 

 to the anterior sacro-iliac ligament. 



