352 

 1916. The skull of a Hare (Lepus timidus). 



In few Mammalia is this part of the skeleton more remarkably modified than in the Hare. 

 The superoccipital is surmounted by a square platform of bone originally a distinct inter- 

 parietal the posterior angles of which project backwards in the form of two tubercles, from 

 between which a vertical crest descends to the foramen magnum. The paroccipitals arch down- 

 wards and outwards in close connection with the descending process of the large subquadrate 

 mastoid, which anchyloses with the petrosal and tympanic. The long bony ' meatus audito- 

 rius' ascends obliquely backwards the direction in which this timid Rodent is most concerned 

 in ascertaining the sounds that may warn it of an approaching enemy. The petromastoid is 

 articulated in a peculiar manner to the squamosal, which bone retains more of its normal ele- 

 mentary shape as a diverging appendage than in most other Mammalia. After expanding be- 

 yond its zygomatic part to be applied to the parietal and alisphenoid, the squamosal resumes 

 the form of a narrow thin plate of bone, which is applied to a shallow depression upon the 



, .mas.t<jidi and thus clamps it, as it were, to its place. The frontal sends outwards a large ali- 



i '-' -form 'curved plate above each orbit, the extremities of which form postorbital and antorbital 



: processes',' ttie notches which divide the anterior from the posterior part of the frontal being 



" u'misVi'aJly'deep. The common outlet of the optic nerves extends forwards, so as to occasion 

 a small vacuity at the back part of the interorbital septum. Each orbit presents a wide vacuity 

 at its fore part, which leads into the lateral nasal cavity, bounded externally by the singularly 

 reticulate nasal plate of the maxillary. The zygomatic arch, which is slightly curved down- 

 wards but scarcely at all outwards, developes a small prominence both from its front and hind 

 extremity below the points of suspension. The articular surface for the lower jaw is broad 

 and concave transversely, narrow and convex longitudinally ; the squamosal presents a non- 

 articular fossa behind it ; a small hemispheric condyle of the lower jaw is applied to it. The 

 bases of the sockets of the superior molars form a strong prominence in the orbit below the 

 anterior vacuity. The nasal bones are remarkable both for their length and breadth : they 

 extend further back than the long slender nasal processes of the premaxillaries. The bony 

 palate is extensively encroached upon by the prepalatal apertures, which blend together to 

 form a narrow heart-shaped vacuity with the apex directed forwards, largely exposing the 

 vomer and the nasal cavities. The palatal processes of the maxillaries and palatines form a 

 bridge, or platform, extending across opposite the three anterior molar teeth. The nasal pro- 

 cesses of the palatines are of unusual height. The anterior incisors have the usual curvature 

 and scalpriform structure of the Order, but are relatively smaller than in the more typical 

 Rodents : they are longitudinally and deeply grooved anteriorly. The second incisors, 

 peculiar to the Family Leporidae, are small and simple, placed immediately behind the first, 

 sening as a kind of anvil, or point of resistance, to receive the appulse of the summits of the 

 inferior incisors. The angle of the lower jaw forms a broad compressed plate, with the lower 

 border rounded and thickened, so as to project a little beyond both the outer and inner sur- 

 face of the ascending plate : the outer ridge is continued forwards to the horizontal ramus, 

 bounding the large masseteric fossa. The petrotympanics form 'bullae ossese.' The ptery- 

 goids develope both external and internal plates : the outer plate is widely perforated at its 

 base ; the inner plate terminates in a hamular process. 



In the common foramen opticum, the wide palatal vacuities, the transversely extended 



