142 THE AETICVZATIONS. 



is confounded in front with that of the opposite side. The inferior 

 portion, the inferior stellate or costo-sternal ligament, is in relation with the 

 pectoral muscles. ^ 



Synovial capsule. — There is one for each articulation. 



Characters proper to the first costo-sternal articulation. — The first costo- 

 sternal articulation is not separated from its fellow of the opposite side ; so 

 that these two joints are, in reality, only one, and the two cartilages lying 

 close to each other correspond by a small diarthrodial facet, continuous with 

 that for the sternum. The two sternal facets are inclined upwards, and 

 confounded with one another. Only one synovial cavity exists for this 

 complex articulation, which unites the two first ribs to each other and to the 

 sternum. 



3. Chrondo-eostal Articulations uniting the Bibs to their Cartilages. 



These are synarthrodial articulations whose movements are very obscure. 

 They are formed by the implantation of the cartilages in the rugged cavities 

 the ribs present at their inferior extremities. The solidity of these articu- 

 lations is assured by the adherence of the fibro-cartilage to the proper 

 substance of the ribs, and by the periosteum which, in passing from the 

 bone to the cartilage, plays the part of a powerful peripheral band. 



In the Ox, the sternal riba, in xmiting with theii' cartilages, form a veritable 

 ginglymoid diarthrosis, whose movement is facilitated by a small synovial capsule. 



4. Articulations of the Costal Cartilages with each other. 



The ribs, attached to each other by means of the intercostal muscles, are 

 not united by real articulations ; neither are their cartilages of prolongment. 

 But the asternal cartilages are bound together by a small yellow elastic 

 ligament, which is carried from the free extremity of each to the posterior 

 border of the preceding cartilage ; the anterior border of the first asternal 

 cartilage is directly united to the posterior border of the last sternal cartilage, 

 through the medium of the perichondrium and very short ligamentous bands. 

 This same asternal cartilage is also bound to the inferior face of the xiphoid 

 appendage by a small white ligament (the chondro-xiphoid), under which 

 passes the anterior abdominal artery. 



5. Sternal Articulation peculiar to the Ox and Pig. 



It has been already shown that in these animals the anterior piece of the sternum is 

 not consolidated with the second portion. The two are united by a, diarthrodial 

 articulation ; and for this purpose the anterior presents a concave surface, the posterior 

 a convex one. Bundles of peripheral fibres firmly bind them to each other, and a special 

 small synovial capsule facilitates their movements, which are very limited. 



6. The Articulations of the Thorax considered in a general manner in regard to 



Movements. 



The thorax can increase or diminish in diameter in an antero-posterior 

 and a transverse direction ; whence arises the dilatation and contraction 

 of this cavity : the inspiratory movements accompanying the entrance of the 

 external air into the lungs, and the expiratory movements expelling the air 

 contained in these organs. 



The variations in the antero-posterior diameter of the chest being due to 

 changes in the figure of the diaphragm, need not be noticed here. But the 

 transverse variations being the result of the play of the costal arches on the 



