44 Anatomy of Skeleton 



II. SECONDARY. 



(a) (Constant). 



Upper and lower epiphysis for each body . . .10 

 Epiphysial plate for auricular surface ... 2 

 Epiphysial plate for margin below this ... 2 



14 



(b) (Variable). 



Epiphysial tips for spinous, transverse, and mammil- 



lary processes. 

 Additional centres for the margins. 



The fusion of all these component parts commences in the lateral region, where 

 the costal elements join the neural arches before the sixth year. A little later the 

 arches and costal bars join the centre, the more distal ones fusing first. As soon as 

 this has occurred, the laminae commence to unite from before backward, completing 

 the process at puberty, and then the costal processes unite with each other distally. 



After this the epiphysial plates of the bodies commence their junction, from below 

 upwards, the process not being completed until twenty-five. 



Lastly, about this time, the lateral epiphysial plates and the remaining secondary 

 centres consolidate with the bone. 



COCCYX. 



This small bone is composed of the fused remains of four or more vertebral bodies, 

 of which the first alone, as a rule, carries rudiments of transverse processes and upper 

 articular processes : the latter are termed cornua, and are attached by ligaments to 

 the sacral cornua. The upper surface of the first coccygeal body articulates with the 

 lower end of the sacrum with intervening fibro-cartilage. The number of segments 



in the bone is variable, and may 



ror 



s * r or ln women 



rrdns.pr. ~J yj&//////ffij\ r |,TnTTTT7r77;7 v_ and four or more in men, speaking 



generally : ventral processes have 

 keen described as occasionally 

 present, representing either costal 



, , 



elements or the remains of haemal 



FIG. 35-Coccyx. archeS ' 



The first segment is often 



separate, the others more rarely : fusion is said to take place later in women, no 

 doubt in accordance with the functional requirements of the pelvic outlet. 



The last segment represents the fusion of three or more rudiments that are present 

 in the embryo : it is the extent of this fusion that determines the number of segments 

 present in the adult bone : the fourth segment is frequently larger than the third. 



The bone is directed forwards and downwards from the sacrum, so that its ventral 

 surface looks upwards and forwards. The muscular floor of the pelvis reaches its 

 margin, and ligamentous fibres from this and the lesser sciatic ligament run on to its 

 front surface and cover it, with the fibres of the anterior ligament : these separate it 

 from the coccygeal ganglion and the rectum (Fig. 35). The great sciatic ligament 

 and Gluteus maximus reach the margins behind the structures already mentioned, 

 and fibres from these spread over the dorsal surface of the bone, covering in the filum 



