350 DK. G. ELLIOT SMITH ON 



In this family we find almost a complete sei'ies of intermediate forms between the 

 small brain of Chlumydophoras, which is but 17 mm. long- and broader than it is long, 

 and the laro-e brain of Priodon, which is not very different in size from those of Ilijrmcco- 

 phaga and Oyijcteropus, and has cerebral hemispheres not unlike those of the larger 

 Ant-eaters in shai)e. Between the short broad type of hemisphere of CJilamydopJwrus 

 and the long and relatively narrow type of Priodon, we find within this family all 

 intermediate gradations. In Xenurus and Tatusia the short square form is not yet 

 lost, while in Toli/peutes and Dasijpus, especially the species sexciiictus, we fi.nd a 

 decidedly elongate type of hemisphere making its appearance. The transition from the 

 hemisphere of Dasi/p)us sexciiictus to that of Priodon is practically a question of mere 

 increase in size. 



In spite of these great variations in external form, there are obvious signs of the 

 family resemblance in the configuration of the pallium. Such being the case, it is 

 of interest to note how much cerebral form may become modified in one homogeneous 

 family. This fact emphasizes the extreme caution which should be exercised in drawing 

 conclusions from the mere shape of the cranial cavity of fossil forms. 



In the small brain of Chlami/dojihorns, which lacks even a rhinal fissure, it is not 

 surprising to find a complete absence of sulci in the small pallial area. The only fissure 

 in the hemisphere of this peculiar Armadillo is the hipj)ocampal, which is absolutely 

 constant in all mammals, and is never found outside the Mammalia. 



I have already had occasion to call attention to a small pallial sulcus, distinguished 

 as /3, which is present in all the Armadillos except Cldauiydopliorus. This sulcus is 

 sometimes continuous with the posterior rhinal fissure, as, for instance, in Dasypus ; 

 at otlier times it is separate, as in Tatusia. It is not unlikely that this small sulcus is 

 the homologue of a n.ore extensive sujiraorbital sulcus (/3), which the ancestors of the 

 Dasypodidce possessed. In this case a small area immediately below the point of junction 

 of the sulcus in question and the posterior rhinal fissure might be regarded as the 

 analogue of the fossa Sylvii. 



Tiie disposition of this sulcus (lig. 10), its position on the hemisphere, and its relation 

 to the rhinal fissure all support the analogy to the sulcus /3, which I have suggested. 



In addition to the pallial sulcus /3, there is in Uakypms (fig. 11), Tatusia (fig. 13), and 

 sometimes in Xenurus a second pallial sulcus, which extends obliquely upward and 

 backward from a point just above the junction of the posterior rhinal fissure with the 

 sulcus /3. The presence of this sulcus in the genera Dasypus and Tatusia and its 

 constancy, indicate that it is a feature of some niorjdiological importance. It is not 

 improbable that we must look to the suprasylvian sulcus (o) of other families for the 

 homologue of this, which we have distinguished as o in the Armadillo. In a brain 

 with a reduced pallium such as that of the Dasypodidce the suj^rasylvian sulcus, which 

 we have already learned to regard as having considerable morjihological importance and 

 as appearing early in phylogeny, would probably occujjy the situation which the sulcus 

 g occupies in Dasypus. 



It is particularly unfortunate that the only brain of the Dasypodidce Avith which we 

 are not acquainted is that of the Giant Ai'madillo [Priodon), because it is highly probable 



