69 



to the third lumbar, has been broken away from the rest of the sacrum. 

 The extent of the ossified intervertebral substance which connects the 

 lumbar vertebrae with each other and with the sacrum is clearly defined 

 on the floor of the spinal canal. The body of each lumbar vertebra is 

 perforated in the centre by a vertical vascular canal ; that of the middle 

 lumbar is the largest and most regular in its form ; it bifurcates near 

 its lower extremity. The gradual expansion of the capacious spinal 

 canal as it approaches the sacrum is deserving of notice in this speci- 

 men ; as also the sudden dilatation in the canal or foramen for the last 

 lumbar nerve, corresponding with the large ganglion of the posterior root 

 of that nerve. Purchased. 



399. The proximal end of one of the posterior vertebral ribs, showing a single 

 articular surface upon the head. Purchased. 



400. A fragment of a vertebral rib of the Mylodon robustus. Purchased. 



401. An ossified sternal rib of the Mylodon robustus, wanting the end which 



articulates with the vertebral rib, but having two distinct articular sur- 

 faces at the sternal end, and showing also a portion of the flat articular 

 surface for the adjoining sternal rib. Purchased. 



402. The sternal extremity of a sternal rib of the Mylodon robustus, showing 



two distinct articular surfaces ; the upper one is again subdivided into 

 two, for the complicated joint with the sternum. Purchased. 



403. The sternal end of a sternal rib of the Mylodon robustus, showing two 



articular surfaces for the sternum. Purchased. 



404. The sternal extremity of a sternal rib of the Mylodon robustus, showing 



two articular surfaces for the sternum. Purchased. 



405. A similar specimen. Purchased. 



406. A similar specimen. Purchased. 

 407- A portion of a sternal rib of the Mylodon robustus. Purchased. 

 408. One of the sternal ribs of the Mylodon robustus, showing the flat sub- 



