32 



Anatomy of the Rabbit. 



In a comparison of the adult skeleton with the more primitive 

 embryonic skeleton, several differences in the arrangement of the 

 elements are evident. Thus many bones, notwithstanding their 

 possession of several centres of ossification, are to be looked upon as 

 individual either in the cartilage or in the bone condition. In other 

 cases, as in the basal portion of the skull, separate bone elements 

 are produced in a mass of cartilage primarily continuous. These 

 either remain distinct throughout life, or, as in the occipital region, 

 (Fig. 12), become fused together to form compound or composite 

 bones. In still other cases, as in the vertebrae, the apparently 

 single elements of the adult condition are the products not only of 

 originally distinct bones, but also of primarily separate cartilage 

 masses. 



Fig. 13. Vertical sections of elbow and knee of four-day-old rabbit. A. 

 elbow; c, capsule; eb, endochondral bone in the distal epiphysis of the humerus; 

 ea, extensor muscles of the forearm; em, extensors of the hand; fa, flexors of the 

 forearm; fm, flexors of the hand; h, humerus; ol, olecranon; r, radius; sc, 

 synovial cavity; u, ulna. B, knee; a, anterior cruciate ligament; c, capsule; 

 f, femur; lp, patellar ligament; p, posterior cruciate ligament: pv. popliteal 

 vessels; t, tibia; x.x, anterior and posterior ligaments of the lateral meniscus; 

 x',x\ anterior and posterior ligaments of the medial meniscus. 



The bones of the skeleton are united or articulated with one 

 another by connective tissue in the form of ligaments, by c artilag e, 

 or in some cases by both together, i.e., by nbrocartilage. Liga- 

 mentous union, distinguished as syndesmosis, is the most general 

 type of articulation. Cartilage union or synchondrosis occurs 

 in certain situations, as in the basal region of the skull. Union by 

 nbrocartilage or symphysis is characteristic of the articulation 

 of the two sides of the pelvis (symphysis pubis). ■ 



