84 



•walls of the cranium, are of large size ; no orbits proper are defined in 

 the general orbital space, owing to deficiency of both pre- and post-or- 

 bital processes. The dome of the cerebral cavity is bat little inflated ; 

 its sides seem somewhat pinched, there being a decided though shallow 

 concavity just above the zygomatic spur of tbe squamosal ; and a slight 

 bulging anteriorly on each side at the usual site of post-orbital processes. 

 The median line of the cerebral roof, in an old Geomys skull, is a ridge; 

 this ridge bifurcates anteriorly to send a curved leg forward and out- 

 ward to the orbital margins; and behind enlarges a little to receive a 

 small interparietal. In various TJiomomys sknUs of different ages the squa- 

 mosals leave a rectangular interval occupied by small narrowly linear 

 parietals; and, instead of a single median ridge, there are two parallel 

 ridges with a depressed interval. The sides of the rostrum are straight 

 and parallel, the edge being the swollen track of the superior incisors. 

 The end is vertically truncate, the tips of the nasals and intermaxillaries, 

 and the faces of the incisors being all about in one perpendicular plane. 

 The width of tlie rostrum is rather more than half its length. 



Viewed in profile, the skull shows an almost perfectly straight dorsal 

 outline from the occipital protuberance to a point just in advance of the 

 orbits. Here is the highest point of the skull, whence the profile of the 

 rostrum slopes gently downward, ending abruptly by vertical truncation. 

 Likewise, the posterior or occipital outline is straight, or nearly so, 

 and at a right angle with the superior surface. Likewise, again, the in- 

 ferior surface of the skull, in all that part lying behind the pterygoids, 

 presents a nearly straight and horizontal profile, at right angles with 

 the occipital plane. Neither bulla ossea nor paroccipital nor condyle 

 is sufficiently developed to interfere with the straightness of outline and 

 rectangularity which all the back part of the skull presents to the 

 side view. The rest of the under outline of the skull consists of the 

 palatal profile as a whole. This consists, anteriorly, of a deep (semi- 

 oval) concavity; there is an abrupt rise from the incisive alveolus, and 

 then a long gradual curve sloping far backward and downward to the 

 molar alveolus ; while the strong obliquity of set of the anterior molars 

 protracts this same curve to the tips of the teeth. The niolar alveolar 

 border is very short, and rather oblique, being lowest behind. The 

 enormous arched interval between the incisors and molars is highly 

 characteristic, as is also the low position of the molars — the teeth dip 

 below a line drawn from the tips of the incisors to the foramen magnum. 

 Behind the palate, flange-like pterygoids slope up to the basi-occipital 

 plane. In this view, the zygomata are seen to dip but slightly down- 

 ward. Their point of greatest deflection lies high above a line drawn 

 from the incisive alveolus to the occipital condyle — in fact, even above 

 a line from the end of the nasal bones to the same point ; at their lowest 

 point, they are still on a level with the meatus, and they scarcely dip 

 more than half-way from the top of the skull to the level of the molar 

 crowns. For the rest, notable points of the profile view of the skull are 

 the small size and peculiar position of the " anteorbital " foramen, here 

 situate low down and far forward in the maxillary, near its antero- 

 inferior angle ; a deep pit, but not perforation, behind the zygomatic 

 plate of the maxillary; extensive lacerate foramina of exit of nerves 

 entering the orbit from the brain; similar fissured vacuities between 

 the bulla ossea and the squamosal. The foreshortened tubular meatus 

 is seen in the deep recess between the posterior root of the zygoma and 

 the postero-inferior angle of the squamosal. 



VieAved from behind, the occipital surface is seen to be nearly plane 

 and vertical, with some beveling of the lateral (mastoid) j)ortions. The 

 most remarkable feature is the extent of this surface which is formed 



