MICROTUS 665 



wall of canal I'udimentary below, absent above. Rostrum slender, 

 scarcely wider than interorbital region, rather deep proxinially 

 but shallow anteriorly, the least depth behind incisors slightly 

 greater than width in same region ; nasals broad anteriorly, 

 abruptly narrowed at middle, the posterior termination pointed, 

 blunt, or angular-emarginate, seldom extending behind level of 

 middle of zygomatic root, and usually a little exceeded by nasal 

 branches of premaxillaries ; incisive foramina long and narrow, 

 slightly narrower posteriorly than anteriorly, extending from about 

 3 mm. behind incisors almost or quite to level of molar alveoli. 

 Palate rather narrow (less than twice width of alveolus), marked 

 by two longitudinal grooves continued back from incisive foramina 

 to lateral bridges of posterior border ; median posterior ridge and 

 lateral pits well defined, the anterior border of pits on level w^ith 

 first inner re-entrant angle of m^. Mesopterygoid space narrow, 

 about 2^ times as long as wide, the pterygoids and hamulars 

 straight. Ectopterygoid plate well developed, the ectopterygoid 

 pit large and deep, not encroached on by bulla. Mandible robust, 

 the portion in front of molars short ; masseter ridge well developed ; 

 coronoid process large, its base broad, its extremity rising to level 

 of condyle and distinctly curved backward ; articular process 

 abruptly bent inward at level of base of incisor, the root of 

 which does not as a rule, however, produce any marked swelling 

 on outer side of process ; angular process well developed though 

 rather slender, curved strongly outward. 



Teeth. — Upper incisors robust, strongly curved, the shaft 

 forming almost exactly half a circle, the root producing a slight 

 protuberance in lower portion of anteorbital foramen, the exposed 

 part of tooth directed downward with a slight backward curve, 

 the anterior face barely visible when skull is 

 viewed from above ; section of shaft obscurely 

 triangular with broadly rounded angles, the 

 anterior face longest, the inner face nearly as 

 long as anterior face, the postero-external 

 face noticeably shorter than either of the 

 others ; enamel covering entire anterior face 

 and extreme anterior portion of inner face ; 

 cutting area rather deeply but simply hol- 

 lowed, the anterior (enamel) edge entire and 

 nearly straight when viewed from in front, 

 obliquely flattened and with rather abruptly y^^ -^g^, 



backward-curved extremities when viewed Microtus agrestic. 

 from below, the posterior edge usually with Enamel pattern, x 5. 

 some irregular notches cut by the points of 

 the lower teeth. Lower incisors much less strongly curved 

 than upper incisors, their roots extending into base of articular 

 process of mandible but not producing any noticeable swelling 

 on outer surface ; section of shaft much like that of upper 

 incisor, but antero-posterior diameter relatively greater, and 



