COST^ AND C0STICARTILA6INES. 165 



and pull ventro-cephalad. This will show the way in which the 

 capacity of the thorax is increased. 



§ 433. Arthra — Joints. — Remove the muscles covering the tu- 

 berculum and cervix of the seventh rib for example, and the liga- 

 ments will be seen as white bands holding the tuberculum to the 

 diapophysis and the capitellum in the socket formed by the demi- 

 facets of the two vertebrae (Fig. 52, Srthron capitelU). Cut away the 

 ligaments on the caudal side of the tuberculum with the arthrotome 

 and bend the rib cephalad. This will expose the smooth arthral 

 surface of this diarthrodial joint. That of the capitellum may be 

 demonstrated in the same way. 



To demonstrate the ampMartJirodial joints at the arthron costi- 

 cartilaginis, the finger or some solid substance should be placed 

 entad of the arthron, and then the ectal surface of the bone and car- 

 tilage should be sliced away with the arthrotome. The cartilage 

 and bone will be found continuous, the ends not being separate 

 and smooth for gliding upon each other as with the capitellum 

 and tuberculum. The end of the rib is but very slightly hollowed 

 out to receive the cartilage, thus differing from the condition in 

 man, where the cartilage is implanted in a deep pit. 



The diarthrodial joints of all the sternal ribs (8 or 9) at the junc- 

 tion of the costal cartilages and sternum (§§ 424, 430), may be dem- 

 onstrated by slicing off the ectal surface of the conjoined sternum 

 and cartilage as directed for the Arthron costicartilaginis. 



§ 484. Ligamentum interarticulare — Interarticular ligament 

 (Pig. 50). — This is most satisfactorily demonstrated in one of the 

 middle ribs, the seventh for example. The muscles should be re- 

 moved as for demonstrating the tubercular and capitellar joints, 

 and the ligaments binding the tuberculum to the diapophysis should 

 be cut. Nip away the neural arch (Fig. 53) and remove the short 

 segment of exposed myelon. This will expose the floor of the neu- 

 ral canal. Dissect the dorsal (posterior) common ligament from the 

 intervertebral fibro-cartilage, move the rib, and the ligamentum 

 interarticulare will be seen, as a rope in a pulley, passing across 

 the floor of the neural canal in a groove on the dorsal surface of the 

 intervertebral fibro-cartilage, and connecting the heads of the pair 

 ofribs(§444). 



§ 435. This ligament differs so remarkably from its homologue in man that a brief com- 

 parison is added : — 



In man the ligament is plate-like. In the cat it is thick and band-like. In man it 



