ON THE EPISTERNAL APPARATUS OF MAMMALS. 557 



peculiarly formed clavicle is no more immediately connected with the 

 manubrium sterni, than was the case in the above-mentioned animals. 

 The terminal surface presents a saddle-shaped depression which, for 

 the anterior third of its extent is iuA^ariably directly attached to a 

 remarkable cartilaginous structure {ep)^ whilst in the posterior two- 

 thirds, an articular cavity frequently intervenes. The cartilaginous 

 piece is at least equal in length to one-third of the clavicle, and is 

 applied to the anterior and lateral borders of the manubrium sterni. 

 The extent of the joint between the clavicle and the cartilaginous 

 piece varies to some extent according to my observations, and in a 

 few examples appeared only as a small fissure extending from behind 

 forwards. The whole sterual end of the clavicle is invested by a thin 

 cartilaginous layer, which at the part corresponding to the joint 

 forms an articular cartilage, covering the clavicle, whilst elsewhere it 

 is directly continuous with the cartilaginous episternal piece, though 

 the limits of the two in a histological point of view are sharply 

 defined. The structural characters of the cartilaginous piece itself 

 cause it to be just as strongly differentiated from the manubriimi 

 sterni as from the clavicle : and the surface of the former seems also 

 to be invested by cartilage. As regards the intimate structure of 

 the episternal cartilage, I found that with low microscopical powers, 

 it presented a peculiar longitudinally striated appearance, just as 

 though a fibrous investment was continued over it, from the clavi- 

 cular to the sternal extremity. Closer investigation, however, 

 showed that this apparent fibrillation was in reality due to the peculiar 

 arrangement of the morphological elements of the cartilage. For 

 immediately beneath the surface of the sternal extremity, roundish 

 scattered cartilage cells appeared, which occasionally presented indi- 

 cations of division. At a short distance from this point, and towards 

 the middle of the cartilage, the cells formed rows, at first of a some- 

 what oval form, and composed of three or four cells, but subsequently 

 of a greater number, as ^vhm ten to fifteen, the group then presenting 

 a fusiform shape. By comparing different rows, it was ascer- 

 tained that each row proceeded from a single cell, multiphcation by 

 division in a longitudinal direction being exceedingly common amongst 

 them. The intermediate substance (matrix of the cartilage) showed 

 also some indications of longitudinal striation, though no doubt the 

 impression to the eye was chiefly the result of the above-mentioned 

 arrangement of the cells. The external investment of the cartilage, 

 composed of connective tissue, was continued from the periosteum of 



