STRUCTURE AND COMPOSITION OF CARTILAGE. 



157 



Fig. 54. 



the ribs, we find canals excavated at wide distances from each other ; which 

 are lined by a continuation of the perichondrium or investing membrane of 

 the cartilage, and which thus allow 

 its vessels to come into nearer prox- 

 imity with parts, that would be other- 

 wise too far removed from them. 

 The vessels, however, nowhere pass 

 from the walls of these canals into 

 the substance of the cartilage. Si- 

 milar vascular canals are found in the 

 temporary cartilages, near the points 

 where the ossifying process is taking 

 place ; this is well seen in the long 

 bones, towards their extremities. At 

 an early period of foetal life, there is 

 no distinction between the cartilage that is ultimately to become the Osseous 

 Epiphysis, and that which is to remain as Articular Cartilage ; both are alike 

 cellular ; and the vessels that supply them with nutrient materials penetrate 

 no further than their surfaces. At a subsequent period, however, when the 

 ossification of the epiphysal cartilage is about to commence, vessels are 

 prolonged into it ; and a distinct line of demarcation is seen betwixt the vas- 

 cular portion, which is to be converted into Bone, and the non-vascular part, 

 which is to remain as Cartilage. At this period, the Articular Cartilage is 



Fig. 55. 



Vessels between the Articular Cartilage and attached 

 Synovial Membrane. (After Toynbee.) 



Vessels situated between the attached synovial membrane, and the articular cartilage, at the point 

 where the ligamentum teres is inserted in the head of the os femoris of the human subject, between the 

 third and fourth months of fetal life ; a, the surface of the articular cartilage ; 6, the vessels between the 

 articular cartilage and the synovial membrane ; c, the surface to which the ligamentum teres was at- 

 tached ; d, the vein ; e, the artery. 



nourished by a plexus of vessels spread over its free surface, beneath its sy- 

 novial membrane; as well as by the vessels, with which it comes in contact 

 at its attached extremity. Towards the period of birth, however, the sub-sy- 

 novial vessels gradually recede from the surface of the articular cartilage ; and 

 at adult age they have entirely left it, though they still form a band which 

 surrounds its margin. The Fibrous cartilages are somewhat vascular ; but 

 the vessels do not extend to the cellular portions, where such exist. 



189. No vessels can be traced (according to Mr. Toynbee) into the sub- 

 stance of the true Cornea ; which, contrary to the statement of Miiller, is a 

 cellular rather than a fibrous cartilage. The cells are not so numerous as are 

 those of the articular cartilages; and they are surrounded by a plexus of bright 

 14 



