No. 545] ORIGIN OF UNIT CHARACTERS 



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the facial or preorbital region shows intermediate or 

 partly blended form and proportions both of the nasals, 

 premaxillaries, frontals, and lachrymals, in which, how- 

 ever, the mule approaches E. caballus rather than E. 

 asinus. Attention may be called to some of the details 

 of the comparison: (1) Suture between the nasals and 

 premaxillaries: in E. asinus short and elevated, in the 

 mule intermediate but more like the horse ; in the horse 

 elongated and depressed (see Fig. 5). (2) Naso-frontal 

 suture on the top of the skull: in the ass straight or trans- 

 verse ; in the mule incurved, more like the horse than the 

 ass; in the horse arched or incurved (see Fig. 6). (3) 

 Depth and convexity of the nasals: in the ass shallow and 

 flattened ; in the mule deeper, more like the horse ; in the 

 horse highly arched. (4) Bump or convexity on posterior 

 third nasals: in the ass very slight; in the mule moderate, 

 more like the horse than the ass ; in the horse strong (see 

 Fig. 7). 



The same tendency in the mule to exhibit a slight de- 

 parture from the horse toward the ass type is shown in 

 the outlines of the bones of the face (Figs. 3, 4, 5). Com- 

 paring step by step the premaxillaries, maxillaries, 

 nasals, and lachrymals, while the proportions and the 

 sutural outlines are mainly those of the horse, there is a 

 more or less distinct blending, or intermediate character 

 in the direction of the ass ; see especially the naso-pre- 

 maxillary suture, the degree to which the nasals extend 

 downward on the sides of the face to join the maxillaries, 

 and the degree to which the nasals extend on the sides of 

 the face to join the maxillaries. In this nasomaxillary 

 junction certain horses approach the ass type. The char- 

 acteristic bump on top of the nasals of the horse is trans- 

 mitted to the mule, and the highly characteristic trans- 

 verse suture between the frontals and the nasals, as seen 

 from the top (Fig. 4), is rather that of the horse than of 

 the mule. 



Non-blending.— More definite results are shown m the 



