52 



this respect, as has been already observed, the ribs of the Elephant itself. All 

 the ribs are articulated to the vertebrae by a head and tubercle, separated by 

 a neck, which is longest in the middle pairs of ribs : the head abuts against and 

 crosses the vertebral interspace, where it is articulated by two distinct surfaces ; 

 one terminal, adapted to the surface b in PL VIII. fig. 2, of the antecedent ver- 

 tebra ; the other superior, and received into the cavity a, of the same vertebra, 

 to the transverse process of which the third articular surface on the tubercle of 

 the rib is joined. 



The first rib is more curved than in the large Pachyderms and Ruminants. 

 Its small head stands inwards at right angles to the shaft : this is compressed 

 antero-posteriorly ; the upper half of the anterior surface is traversed by a lon- 

 gitudinal ridge, bounding the outer side of a deep and wide channel, in which 

 the surface of the bone is reticulated. The rib increases in breadth as it ap- 

 proaches the sternum : rough prominences on its outer surface indicate where 

 the ossified cartilage originally began : this, which in its present ossified and 

 anchylosed state forms the sternal end of the rib, was of a quadrate figure, 

 broader than long. It is articulated, by a synovial surface of a narrow oval 

 form, to the manubrium sterni, at the part marked a, fig. 1, PI. IX. The inner 

 surface of the first rib is smooth and slightly convex, except near its posterior 

 margin, where the shallow groove for the intercostal nerve and vessels may be 

 traced. 



The second rib is longer and more slender than the first, but is similarly in- 

 dented by a broad longitudinal groove on its anterior and upper surface, which 

 gradually contracts and disappears as it descends. The superior length of this 

 rib is chiefly due to its ossified and anchylosed cartilage : this contracts and 

 assumes a trihedral form near the sternum, to which it is articulated by two sur- 

 faces in the interspace of the manubrium and second bone*. 



In the third and succeeding ribs, the groove, described as impressing the outer 

 surface of the first and second ribs, runs along the thickened anterior margin, 

 and attains rather the inner side of that margin, in the long posterior ribs. 

 These decrease in thickness to their posterior margin, which is sharp and bends 

 inwards, so as slightly to define the ordinary shallow canal for the intercostal 



* ITie surface on the manubrium for the second rib is shown at fig. 2. c, PI. IX. 



