ARTICULATIONS OF TEE F08TERI0B LIMBS. 159 



becoming confounded with the perforans tendon, the plantar cushion, and the kera- 

 togenous membrane. 



In the Pig, for the maintenance of the second interphalangenl articulation, -there 

 are: 1, Two lateral ligaments, carried from the lateral fuces of the second plialanx to 

 the external and internal faces of the third ; 2, A tiiird ligament, exactly resembling one 

 of tlie posterior lateral ligaments of the pedal articulation of the Horse ; this ligament 

 descends from the inferior extremity of the first phalanx to the internal extremity of the 

 navicular bone. Its analogue of the inner side appears to be altogether absent ; but 

 in the large digits there is an anterior yellow elastic ligament like that of Euminants, 



In the Dog, the two last phalanges are united by two lateral ligaments, very simply 

 arranged. A third ligament, formed of elastic tissue, divided into two lateral portions, 

 and situated in front of the articulation, plays the part of a spring, which mechanically 

 produces the retraction of the claw when the flexor muscles cease to contract. In the 

 Cat, this yellow ligament is very strong ; and this animal also exhibits a very striking 

 obliquity of the articular pulleys by which the two phalanges correspond : an arrange- 

 ment which permits the claw to be lodged between two digits when they are raised, and 

 thus favour its retraction. 



The second interphalangeal articulation of the Dog and Cat is also distinguished 

 by another essential arrangement. Tlie articular surface of the third phalanx is com- 

 pleted by a glenoid fibro-cartilage 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 thu'd phalanx, and serves, by its inferior face, as a pulley for the per- 

 forans 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 of flexion and extension. 



Article V. — Articulations op 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 coxsb.) 



A. Saceo-iliao Articulation (Fig. 90).- — 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," cut 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-ischiatic. 



a. Sacro-iliac ligament. — This is composed of thick fibrcMS fasciculi, 

 which envelope the whole articulation in being firmly attachld by their 

 extremities to the imprints around the diarthrodial facets. The inferior 

 moiety of this ligament is covered by the psoas-iliacus (iliacus) muscle. Its 

 posterior half ^ is much stronger, is hidden by the ilium, and gives attach- 

 ment to the iHo-spinalis (longissimus dorsi) muscle. 



h. Superior ilio-sacral ligament. — A thick and short funicle which, 

 rising from the internal angle of the iUum, 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. — This is a 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 



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

 sponds to the anterior sacro-iliac ligament. 



