446 J. W. HTJLZE ON" IGTJANODOIS' PKE8TWICHII 



its neural arch, plainly rested chiefly on this, its proper centrum, 

 and was only to a very limited extent borne on the last lumbar. 

 The length of the neuro-central suture is only about J of that of the 

 upper surface of the centrum, the attachment being limited behind 

 by the wide groove of exit of the first sacral nerve, which emerges 

 over the side of the centrum rather behind its middle. Behind this 

 nerve-groove is the rough sutural surface descending on the postero- 

 lateral border of the centrum, of which the upper part afforded a 

 limited attachment to the neural arch of the second sacral vertebra, 

 and the lower part formed one side of the notch between it and this 

 latter, where the second lower sacral transverse process was im- 

 planted. This process was evidently smaller than the first. 



In the second sacral centrum (No, 25), the dimensions of the 

 anterior and posterior terminal surfaces do not much, differ. The 

 centrum is evenly and slightly constricted at its middle. The non- 

 articular part or side is cylindroid in the vertical direction, slightly 

 flattened below the neuro-central suture, and again at its under 

 surface, where longitudinally it is concave. It has no median keel. 

 The groove of exit for the 2nd sacral nerve is slightly further back 

 than the corresponding groove in the 1st centrum. The notch in 

 the posterior border of the centrum for the second lower transverse 

 process descends only a slight distance. 



The third sacral centrum (No. 26) differs little from the second. 

 Its under surface is somewhat flatter, and towards the posterior 

 border it has a slight depression. Its lower transverse process is 

 partly borne on the postero-lateral border of the second centrum. 

 The groove of exit for the third sacral nerve is slightly nearer the 

 posterior border of the centrum. 



The fourth sacral centrum (No. 27) is distinguished from the others 

 by the smoothness and concavity of its posterior surface, which 

 evidently allowed the anterior caudal centrum to play upon it 

 through the medium of an ordinary intervertebral disk. The 

 neural arch, rests on the whole length of its own centrum and 

 slightly on the third centrum. The fourth sacral nerve emerged 

 through the intervertebral foramen between it and the first caudal 

 vertebra, and not across the side of its own centrum as in the 

 first three sacral vertebrse. The under surface shows the same 

 flattening and slight hollow noticed in the third centrum. 



With the exception of the anterior surface of the last lumbar or 

 false sacral vertebra, and of the posterior surface of the fourth sacral 

 centrum, all the terminal surfaces of the sacral vertebrse are rough ; 

 their union with one another was evidently too intimate to allow 

 of movement ; and had the animal reached maturity they would 

 probably have become coossified. 



The length of the entire sacrum, including the last lumbar 

 vertebra, is 29 centims., that of the last lumbar being 52 millims. ; 

 of the 1st sacral centrum, 50 millims ; of the 2nd, 63 millims. ; of 

 the 3rd, 49 millims. ; of the 4th, 50 millims. When the centra are 

 articulated the outline of the under surface of the sacrum is ren- 



