586 



ANATOMY OF VERTEBRATES. 



next in advance (or above). The hsemapopliyses, A, are gristly and 

 interposed between the pleurapophyses and the hsemal spines, the 

 conversion of which into the 'sternum' has been already explained. 

 The fact of this short and slender bone in Man being ossified 

 from a longitudinal series of centres (fig. 364, h) is learnt from 

 embryology, the reason from general homology. The haemal 

 spine here repeats the variability of its homotype, the neural one, 

 being sometimes entire, sometimes bifid (ib. c, d). In the three 

 succeeding segments the pleurapophyses become shorter and the 

 haemapophyses are attached by their attenuated ends each to that 

 in advance. In the next two segments the still shorter pleur- 

 apophyses resume the exclusive articulation with their proper cen- 

 trum and terminate freely. The centrum and neurapophyses of 

 each of the segments, with free and elongate pleurapophyses, con- 

 stitute by their coalescence the ' dorsal vertebrae,' which are 

 ' twelve ' in number. Each of the five succeeding^ seorments is 

 represented by the centrum, neural arch, and short confluent 

 pleurapophyses, forming the * lumbar vertebrae : ' the hjemapo- 

 physes of these segments are represented by the ' inscriptiones 

 tendineae musculi recti,' h', which are the homologues of the gristly 

 or bony * abdominal ribs ' of reptiles. The constitution of the 

 Human 'os sacrum' has already been given. Part of a sacral 

 pleurapophysis expands to form the * ilium,' fig. 403, 62, pi. Two 

 haemapophyses called " ischium,' 63, and pubis, 64, coalesce with 

 62 to constitute the ' innominatum : ' the inverted arch, supporting 

 the appendage which becomes developed into 'pelvic limb,' is 

 completed by the ischio-pubic symphysis. 



406 



Kestoration ot Arrhro/itert/.r, n iiiesozoic 



*¥V*'V* . ' 



