190 THE ARTICULATIONS. 



Inter-hyoideal Articulations. — A. The great cornu articulates with the 

 small one, by an amphiarthrosis analogous to the preceding. To form this articu- 

 lation, these two pieces of bone are joined at an acute angle, through the medium 

 of a more or less thick cartilaginous band, in the centre of which there is often 

 a little bony nucleus— the styloid nucleus, or kerato-hyal bone. This cartilage is 

 elastic and flexible, and permits the opening and closing of the articular angle at 

 the summit of which it is placed. 



B. Each styloid cornu is united to the body of the hyoid bone, or basihyal, 

 by an arthrodial articulation. The articular surfaces are : for the hyoideal 

 branch, the small cavity terminating its inferior extremity ; for the body, the 

 convex lateral facet situated at the origin of the thyroid cornua. These surfaces 

 are covered by cartilage, and enveloped by a small synovial sac and a peripheral 

 fibrous capsule. They can ghde on each other in nearly every direction. (Median 

 and superior hyoideal capsular ligaments are described by Leyh as sometimes 

 present. The latter unites the upper and middle branches, and the former the 

 middle with the inferior branches. They are absent when these branches are 

 confounded with the superior ones.) 



Article III. —Articulations of the Thorax. 



These are also divided into extrinsic and intrinsic. The first — named costo- 

 vertebral— unite the ribs to the spine. The second join the different bones of the 

 thorax together ; they comprise : 1. The chondro-sternal articulations, 2. 

 Chondro-costal articulations. 3. The articulations of the costal cartilages with 

 each other. 4. The sternal articulation perculiar to the larger Ruminants and 

 the Pig. All these joints will be first studied in a special manner, then examined 

 in a general way as to their movements. 



Extrinsic Articulations. 



Articulations of the Ribs with the Vertebral Column, or Costo- 

 vertebral Articulations. 



(Preparation.— This is simple. No difficulty need be experienced except in exposing the 

 interartieular ligament, and this is efifected by sawing tlirough one of the dorsal vertebra 

 transversely, close to the posterior intervertebral joint formed by that bone. A few cuts of the 

 bone forceps will then show the whole extent of the ligament.) 



Each rib articulates with the vertebral column by two points — its head and 

 its tuberosity. The first is received into one of the intervertebral cavities 

 hollowed out on the sides of the spine, and is therefore in contact with two doi-sal 

 vertebrfe ; the second rests against the transverse process of the posterior vertebra. 

 From this an'angement arises two particular articulations belonging to the 

 arthrodial class, which are named costo-vertehral and costo-transverse. 



Costo-vertebral Articulations. — Articular surfaces. — Pertaining to the 

 rib, we have the two convex facets of the head, separated from each other by a 

 groove of insertion, and covered by a thin layer of cartilage. On the vertebras, 

 the concave facets which, by their union, form the intervertebral cavity ; these 

 facets are also covered with cartilage, and separated, at the bottom of the cavity, 

 by the con'esponding intervertebral disc. 



Mode of union. — 1. An interartieular ligament (Figs. 126, 2 ; 127, 1), fixed 

 in the groove in the head of the rib, and attached to the superior border of the 



