172 ELEMENTARY BIOLOGY. [CHAP. 



other hand, passes upwards and, curving backwards, becomes 

 attached to the dorsal part of the outer face of the periotic 

 capsule. 



Meckel's cartilage, articulated to the free end of the sus- 

 pensorium, is unossified throughout the greater part of its 

 extent, no osseous articulare being developed; but, at its 

 symphysial end, each cartilage becomes ossified, and forms 

 the mento-Meckelian element of the mandible. 



The slender, cartilaginous band (cornu of the hyoiff) by 

 which the body of the hyoid is attached to the skull, is con- 

 nected with the periotic cartilage immediately in front of 

 and below the fenestra ovalis. 



The pectoral and pelvic arches (see Laboratory work 

 D. e. g.) are, in the young state, undivided cartilages on 

 each side, and the development of bone in and upon them 

 does not really destroy this continuity, the cartilage persist- 

 ing at the ends of the bones and between them, in the 

 glenoidal and acetabular cavities. 



In like manner, the bones of the limbs consist origin- 

 ally of merely cartilaginous models of the perfect bone; 

 but, as development proceeds, the middle of the cartilagi- 

 nous model commonly becomes invested by a sheath of 

 true bone, while a calcareous deposit takes place in the 

 cartilage close to its growing extremities. As the bone 

 grows, the superadded sheath invades the middle of the 

 cartilage and more or less replaces it; while the terminal 

 portions of cartilage continue to grow and enlarge and the 

 calcareous deposit within them increases, without however 

 reaching their surfaces. Thus one of the larger adult limb- 

 bones, the femur, consists of a median shaft of perfect bone, 

 and of two terminal cones of cartilage, containing calcified 

 epiphyses, enclosed within and more or less overlapping the 

 hollow ends of the shaft. 



