34 PHYSIOLOGICAL SERIES. 



becomes thus occasionally exogenous in the neck, as the neura- 

 pophysis does in the tail. 



In the sacrum, besides the osseous nucleus for the centrum, and 

 for each neurapophysis, one for each pleurapophysis commences 

 about the sixth month close to the fore part of each nervous inter- 

 space, in the three anterior vertebra? ; the lowest appearing last, 

 about the ninth month : the junction of the neurapophyses to 

 form the arch begins in the lowest vertebra first, viz. about the 

 second year, but the first sacral vertebra is not a single piece before 

 the fifth or sixth year. About the sixteenth year the sacral 

 vertebrae begin to coalesce, and the fourth and fifth are usually 

 united by the eighteenth year, the process of union gradually 

 proceeding upwards : the terminal epiphyses of the sacral centrum 

 are formed as in the true vertebrae ; and lateral epiphyses, also, 

 begin to form, one for the ends of the pleurapophyses of the first 

 two vertebrae, and one for those of the last three. The whole 

 sacrum is not consolidated till about the thirtieth year. 

 Each coccygeal vertebra is ossified from a single centre. 



Presented l>y William Lawrence, Esq. 



A. 138. The vertebral column of a mature Human Foetus. The 

 ligamentum commune anterius has been removed, to show 

 the intervertebral substances, which are composed largely of 

 concentric ligamentous fibres, passing between and con- 

 necting the whole of the articular surfaces of the bodies of 

 the vertebrae, as is exhibited in the preceding specimen. The 

 articular processes are connected by another mode of arti- 

 culation, where opposed cartilaginous articular surfaces are 

 simply in contact, being connected to each other by a 

 capsular ligament and synovial membrane. 



The pleurapophysis has been preserved on the left side of 

 the seventh cervical vertebra. The summits of the neura- 

 pophyses are joined by cartilaginous rudiments of the 

 neural spine. Short cartilaginous pleurapophyses extend 

 from the diapophyses of the lumbar vertebrae. They have 

 begun to be ossified in the first three sacral vertebrae. 

 0. C. 247. Hunterian. 



A. 139. The sternum of a Human Foetus of the sixth month, 

 exhibiting the commencement of ossification by four separate 

 points or centres ; that of the manubrium, or first bone, 



