No. 2304. REPTILIAN CHARACTERS IN MAMMALS—WORTAIAN. 5 



which rests upon the anterior end of the zygomatic process of the 

 squamosal and forms the postorbital process of the jugal arch, for 

 the attachment of the postorbital ligament, which connects the tip 

 of the postorbital process of the parietal with the zygoma, thus com- 

 pleting the posterior boundary of the eye cavity. 



Immediately in advance of the bone just mentioned is a broad, thin 

 concave bone which forms the principal part of the floor of the orbit 

 upon the outer side. It is thin and extended outwards in such a 

 manner as to give a characteristic flare to the lower and anterior 

 portion of the floor of the eye cavity. In front it touches the maxil- 

 lary and is continued forwards to articulate with the lachrymal, thus 

 forming the anterior lower free viva of the orbit. 



No less astomiding in the formation of the jugal arch of this remark- 

 able skull is stiU another elem-ent, which occupies a position upon its 

 under surface. It articulates in front with the maxillary, sending a 

 long pointed process forwards upon the outer side of this latter bone 

 at the masseteric ridge, and extending backwards on the underside 

 of the zygoma, beneath the zygomatic process of the squamosal. In 

 its backward extension it reaches the glenoid cavity, and takes almost 

 as great a share in its formation as in the Marsupials. Upon its under 

 surface it is produced into a well-defined sharp ridge, which is a direct 

 continuation of the prominent masseteric ridge or process of the 

 maxillary. Above it is in contact with the so-caUed malar or jugal, 

 and the smaU bone which forms the postorbital process of the jugal 

 arch already described. 



The anterior boundary of the orbit is formed principally by the 

 large lachrymal, which spreads out upon the face, and articulates 

 below with the malar, upon the orbital rim. Above, it articulates 

 with the frontal, and in front with the maxillary. Within the orbital 

 cavity it has the usual relations found in the Macroscelididae, and is 

 perforated by a large lachrymal foramen situated entirely within the 

 orbit. Lying at the angle of junction between the maxillary, frontal, 

 and lachrymal, upon the side of the face, at some distance from the 

 edge of the orbit, is another small bone which is not common in the 

 mammalian skuU. It is of a triangular form, with a relatively long 

 pointed extremity, extending backwards between the frontal and 

 lachrymal, and is equally and symmetrically developed upon the two 

 sides of the skull. 



Near the middle of the lachrymal, on the anterior edge of the orbit, 

 is seen the remains of a suture, which runs forwards more than half 

 the length of the bone and then ceases in such a way as not to divide 

 the lachrymal completely, nor to complete the boundary of another 

 element. No distinct traces of this suture can be made out, however, 

 on the inside of the eye cavity, and if the lachrymal was really divided 



