aa COSTO-STERNAL JOINTS. 263 
The following exceptions to the general plan of rib-articulation indicated above 
must be noted :— 
1. There is no articulation between the eleventh and twelfth ribs and the 
transverse processes of the corresponding vertebre. 
2. The superior costo-transverse ligament is wanting from the first rib, and is 
either rudimentary or wanting in the case of the twelfth rib. 
3. The middle costo-transverse ligament is rudimentary in the eleventh and 
twelfth ribs. 
The ligamentum lumbo-costale extends from the upper surface of the base of the 
transverse process of the first lumbar vertebra to the under surface of the neck of 
the twelfth rib, as well as to the under surface of the transverse process of the 
twelfth dorsal vertebra. 
ARTICULATIONS BETWEEN THE RIBS AND THEIR CARTILAGES. 
Each rib possesses an unossified portion, termed its costal cartilage. As age 
advances, this cartilage may undergo a certain amount of superficial ossification, 
but it never becomes entirely transformed. The line of demarcation between 
bone and cartilage is clear and abrupt, and usually the bone forms an oval cup, in 
which the end of the cartilage is retained by means of the continuity which exists 
between the periosteum and the perichondrium. There is no articulation in the 
proper sense between the rib and its cartilage, although a synovial cavity has 
occasionally been found between the first rib and its cartilage. 
INTERCHONDRAL JOINTS, 
These articulations are arthrodial diarthroses, and they are found between ad- 
joining margins of certain of the costal cartilages, viz. from the fifth to the eighth 
or ninth. The cartilages which thus articulate develop flattened, somewhat conical, 
prolongations of their substance, and thereby the intercostal spaces are interrupted 
where these flat articular facets abut against each other. Each joint is closed 
by a surrounding capsular ligament, the superficial and deep aspects of which are 
specially strengthened by external and internal interchondral ligaments. These 
bands extend obliquely between adjacent cartilages. 
A synovial membrane lines each joint-capsule. 
COSTO-STERNAL JOINTS. 
The upper seven pairs of costal cartilages, as a rule, extend to the lateral 
margins of the sternum (articulationes sternocostales). Of these, the first pair is 
implanted directly upon the manubrium sterni. The ossific process ends abruptly 
in connexion with the rib, and also ceases as suddenly in connexion with the 
sternum, and hence the cartilage does not normally present an articulation at 
either end. 
From the second to the seventh pairs of ribs inclusive, the costo-sternal joints 
are constructed upon the type of arthrodial diarthroses, although, in the case of 
the sixth and seventh cartilages, the joint-cavity is always small, and is frequently 
obliterated. 
The sternal end of each of these costal cartilages presents a slight antero-pos- 
terior ridge which fits into a shallow V-shaped depression upon the lateral margin 
of the sternum. With the exception of the sixth cartilage, the others articulate 
opposite the lines of union between the primary segments of the sternum, whereas 
the sixth articulates upon the side of the lowest segment of the meso-sternum. 
Each joint is enclosed by a capsular ligament, composed of fibrous tissue, attached 
to the adjacent borders of the articulating elements. Specially strong fibres dis- 
tinguish the superficial and deep aspects of the capsule. 
The anterior costo-sternal ligament (lig. costo-sternalium radiatum, Fig. 207) is 
composed of strong fibres which radiate from the anterior surface of the costal 
cartilage, near its sternal end, to the front of the sternum. The ligaments of 
opposite sides interlace with each other, and so cover the front of the sternum with 
a felted membrane—the membrana sterni. 
