OSSEOUS SYSTEM OF MAMMALIA. 



299 



187 



tebrse, figs. 184, and 186, j)l, are subject to slight displacement, 

 and their articulations, like those of the neurapophyses in the 

 Bird's sacrum, extend over the interspace between their own and 

 a contiguous centrum. The hajmapophyses, ib. h, are rarely 

 ossified : the exceptions occur in the lowest subclasses (Duck- 

 Mole, Armadillo, Sloth) : in the Monotremes a portion of cartilage 

 intervenes between the pleur- and hiem- 

 apophyses. Some of the posterior htemapo- 

 physes have no haemal spine, but terminate 

 freely, fig. 187, 7, or in connection with 

 each other. The segments typically com- 

 pleted, as in fig. 184, are called ' vertebra3 

 with true ribs,' those not so completed '^ ver- 

 tebras with false ribs,' in Anthropotomy. 

 The haemal spine of each thoracic seg- 

 ment is separately developed. They 

 commonly remain distinct, fig. 187, 9, 9, 

 forming a chain of ossicles, answering in 

 number to those anterior dorsal segments 

 which they complete : they coalesce with 

 each other in some Mammals, and form 

 collectively the ^sternum.' Only in Mono- 

 tremes is there an episternum, figs. 186, 

 h, c, 187, 9, z, or haemal spine of a cervical 

 segment, to which the clavicles articulate. 

 As the dorsal vertebrae recede in position 

 the pleurapophyses become shorter, return 

 to their proper segment, and usually be- 

 come appended to its diapophysis. When 

 it becomes confluent therewith, or replaces that process, the 

 ' dorsal ' series ends and the ' lumbar ' one, 

 figs.166,/, 183, 1-5, begins. These vertebrae 

 are commonly more numerous in Mammals 

 than in Eeptiles. Their haemapophyses — 

 the abdominal ribs of Reptiles — are re- 

 presented by the ' intersectiones tendineae 

 musculi recti,' &c., the lowest pair are par- 

 tially ossified as ' marsujoial bones,' fig. 187, 

 6, in Lyencepliala. In the Mutilata the 

 ^ sacrum ' is defined by the reappearance of 

 the ossified h^emapophyses, fig. 159,63, of 

 a segment at the end of the trunk. In 

 Cetacea it is suspended beneath its segment, as in Fishes, and 

 may support some rudiment of a pelvic or ventral fin, ib. 65, 66, 



Hseraapopliyses .ind spines of 

 truuk, Mammal. 



Type of pelvic and caudal segment, 

 Mammal. 



