212 TEE ARTIVULATIONS. 



pulleys by which the two phalan^'ps correspoml : an arrangement that permits the claw to be 

 lodged between two digits wlien they are raised, and tlius favour its retraction. 



The second interphalangeal articulation of the Dog an<l Cat is also distinguished by another 

 essential arrangement. The articular surface of the tliird piiidanx is completed by a glenoid 

 flbro cartilage analogous to that of the first articulatiim, but much thicker. Tiiis fibro-cartilago 

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

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

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



The iuterphalangeal articulations of Man are forme<l on the same plan as the metacarpo- 

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

 possess only the two movements o( flexion and extension. 



Aeticle 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 witli 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 arthrodial class. 



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

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

 the analogous facet on the internal face of the ilium. 



Mode 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-sciatir. 

 The firet 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 hgament 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 iUum, in becoming confounded with 

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

 Iwrders 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 ovischiatic ligament (Fig. 140, 2). — This is a vast membranous 

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

 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 hiterosseous sacro-iliac ligament of Man. The inferior half correspouda 

 to the anterior sacro-iliac ligament. 



